SOME PTERIDOSPERM STEMS AND FRUCTIFICATIONS
WITH PARTICULAR REFERENCE TO THE MEDULLOSAE1
ROBERT W. BAXTER2
INTRODUCTION
Theophrastus, one of the first to attempt the classification of plants, recognized
as his major groups, trees, shrubs, and herbs. Although this division was long ago
realized to be an artificial one it nevertheless provided then, as it does today, con-
venient categories for different types of plant habit. Since the study of paleobotany
involves not only the search for the ancestral types of present-day plants but also
attempts to visualize and illustrate the gross appearance of past floras we may still
find it convenient to use these major habit groupings in classifying fossil plants.
We now know that the Carboniferous forests were made up of the tree-like
Pitys, Cordaites, Lepidodendron, Sigillaria and Calamites, which attained diameters
of several feet and reached 100 feet or more in height. Growing among these trees
were numerous plants of creeping, climbing, and shrubby habit, characterized in
general by small stems with little or no secondary growth. It is also generally true
that this last group (ferns and seed-ferns) had developed large leaves or fronds
(megaphyllous) while the larger tree-like plants were generally small-leaved
(microphyllous). The term "microphyllous" is used in this paper in a broad sense to
include not only the groups lacking leaf gaps but also those living and fossil gymno-
sperms (Coniferophyta, Arnold, 1948) in which the seeds are stem-borne (Sahni's
(1920) Stachysperms) and the leaves are small, simple, linear or fan-shaped
growths, borne in dense spirals or whorls on the trunk and branches.
In plant evolution the early development of a single large trunk (tree-like) seems
to have some correlation with microphyllous habit, as the development of numerous
small branches of equal size (shrubby) may be correlated with megaphyllous form.
Accordingly, it seems possible that a classification based on external form and size
may, considered in relation to the origin of plant groups, not be entirely without
some phylogenetic meaning.3 As might be supposed, the larger tree-like fossils
1An investigation carried out in the graduate laboratory of the Henry Shaw School of Botany
of Washington University and submitted as a thesis in partial fulfilment of the requirements for
the degree of Doctor of Philosophy in the Henry Shaw School of Botany.
2Assistant Professor of Botany, University of Kansas, Lawrence.
3While it is not our present intention more than to suggest the possibility of the foregoing state-
ments, there is ample evidence that the Coniferophyta (Ginkgoales, Taxales and Coniferales) have
been trees and microphyllous since their origin from the Pityeae and Cordaiteae in Upper Devonian
and Carboniferous times (Arnold, 1948). The other groups of Carboniferous trees (Calamites,
Lcpidodendron, etc.) are, on the other hand, represented today by only a few isolated genera in
the so-called fern allies. Thus it would seem that the only possible ancestral forms of the mega-
phyllous gymnosperms, and possibly the angiosperms, must be sought in the shrubby, climbing or
herbaceous undergrowth of the Paleozoic forests. In this habit group through profuse equivalent
stem ramifications the telome units would be provided for the development of the large frond and
broad leaf, which when fertile may have evolved into sporophylls or carpels (Wilson, 1942).
Issued September 30, 1949.
(287)


[VOL. 36
288 ANNALS OF THE MISSOURI BOTANICAL GARDEN
have received a proportionate amount of attention and are today relatively well
known. On the other hand, while numerous genera and species of the smaller
plants have been discovered and described, it is becoming increasingly apparent that
the field is open for the discovery of many more. This is due in part to improved
techniques and increasing amounts of research material but probably even more to
the undoubted greater diversity of the smaller plants. Certainly in many forest
areas today, the genera and species of tree-like habit are but a small fraction of the
total flora as compared to those of associated shrubs and herbs. In the present
paper we intend to deal with some of these newly discovered small plants (or plant
organs) which appear to be of pteridosperm affinity.
As is well known to ail palcobotanists, the fragmentary nature of the material
preserved in coal balls makes it necessary to describe the isolated plant organs
(stems, roots, leaves, fructifications, etc.), with the hope that subsequent work
will show their proper assemblage. Thus the seed-ferns as a group were originally
described as the Cycadofilicales on the basis of stem anatomy, which seemed to
combine both fern and cycad characters along with a constant association with
fern-like foliage. It was not until 1905 that seeds were actually found attached to
some of these fronds and the present conception of the groups was created. Even
now the possession of seeds is definitely known for only the genus Lyginopteris
(Calymmatotheca Hoeninghausi) and can only be inferred for the numerous other
stems which have been carried over into the new classification on the basis of their
similar anatomy. Briefly, the characters on which this relationship is based are:
small stems, pith or mixed protostele with exarch or mesarch primary wood, sec-
ondary wood of characteristic angular (in cross-section) tracheids, reticulate-
bordered pitting, usually numerous leaf traces, and an outer cortex containing
vertical or horizontal sclerotic bands. Additional similarities and differences are
shown in the accompanying table which lists most of the better-known pterido-
sperm stem genera.
Our new genus (page 289) is validly included through possession of most of
the above-listed characters although it lacked leaves and may or may not have had
seeds. Its reconstructed habit (plate 5) does, however, show a close flattened
branching pattern which offers implications as to the possible megaphyllous de-
velopment of large fern-like fronds. Such ramification in a single plane, along
with the lack of leaves, is suggestive of the Psilophytales, and it is our opinion that
Microspermopteris may constitute a direct link between that primitive group and
the larger seed-ferns. The constant small size (5 mm. or less) of its stems indicates
that it would at best have been an inconspicuous element of the forest group and
must have been either prostrate or climbing.
The three new species of Medullosa described are of course generically identifi-
able by their polystelic structure as well as by the character of the wood and
pitting and, where the latter tissue is preserved, by the fibrous cortex. Here again
the evidence of size and form seems to indicate that the habit was either creeping
or climbing rather than tree-like.


1949]
BAXTER-FOSSIL PTERIDOSPERMS 289
The two new species of Dolerotheca are offered primarily as a supplement to
Schopf's (1948) comprehensive work on the genus, although we believe our ma-
terial does present some basis for additional phylogenetic interpretation as well as
possible additional support for the more definite connection of the fructification to
the Medullosae.
During the latter course of this study several additional small stems of ap-
parently primitive pteridosperm character have been discovered which we hope to
describe in a future paper. One in particular is of interest since, as in Micro-
spermopteris, it appears to be leafless. Thus at least a part of the undergrowth of
Carboniferous times seems to have occupied a position comparable to that of the
living fern allies in that both present a retention of characters primitive for their
time so that the excellent fossil record of the coal beds may yet provide the missing
links from earlier eras just as those primitive living genera (Lycopodium, Equisetum
and Psilotum) have done in part for thE present-day flora.
Microspermopteris aphyllum, gen. et spec. nov.
The following description is based on a total of eight stems occurring in three
different coal balls. Four stems were followed through one coal ball for approxi-
mately 6 cm. and three stems extended through another ball for approximately 4
cm. The eighth stem was isolated i:i the third coal ball and was cut as a longi-
tudinal section 1 cm. in length.
All material is from the What Cheer Clay Products Co. coal mine, one-half
mile west of What Cheer, Iowa. THis horizon lies in the Des Moines series of the
Pennsylvanian and is accordingly of Upper Carboniferous age.
The stems followed a relatively straight to slightly sinuous course. Mixed
among them were numerous specirr.ens of their smaller, but otherwise identical
branches. The stems are of a constant small size even when maturity is indicated
by considerable secondary growth. The total diameter including cortex and epi-
dermal tissues never exceeds 5 mm., while the single stele averages 2 to 2 2 mm.
The external form of the stems is quite variable, particularly in the smaller
specimens where the transverse configuration is almost "amoeboid" in outline
(fig. 3). The more mature specimens with considerable secondary growth appear
oval to circular in cross-section (figs. 1 and 7).
The primary tissues consist of a protostele in which the large metaxylem
tracheids are divided into groups of 12-14 cells by a radiating network of paren-
chyma, the individual strands of which are usually not more than one cell in thick-
ness and in longitudinal section are :;een to be vertically elongated cells, five to six
times as long as wide. The inconspicuous protoxylem groups are situated on the
periphery of the primary tissue and appear to be exarch though their exact position
is vague due to the very small size of the adjacent innermost secondary wood. The
metaxylem tracheids increase slightly in size towards the center, averaging 150 jp
in diameter as against 50 pL for the secondary wood. All walls of the metaxylem
are reticulately bordered pitted with the opposing orifices at a slight angle to one
another (fig. 12).


[VOL. 36
ANNALS OF THE MISSOURI BOTANICAL GARDEN
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1 VoL. 36
292 ANNALS OF THE MISSOURI BOTANICAL GARDEN
The secondary wood ranges from 3-4 rows in thickness in the young small
stems to around 16 in the larger more mature specimens. The first-formed cells
are quite small, being hardly distinguishable in size from the protoxylem. Their
diameter increases gradually towards the outside but never approaches that of the
metaxylem. Longitudinal sections of the secondary tissue show the radial walls
pitted in the same way as the metaxylem, with a dense reticulum of bordered pits,
while the tangential walls have fewer scattered pits, with more lineal openings,
arranged in irregular rows up and down the central area. Wood rays are incon-
spicuous and relatively sparse. They are small, uniseriate and from I to 4 cells in
height (fig. 9). A rather frequently observed character of the secondary wood of
the mature stems is its unequal development (fig. 7) which is possibly due in some
cases to differing cambial activity and in others represents the unfilled gaps left by
departing branch steles. The tissues immediately surrounding the wood are seldom
well preserved and are represented in all of our specimens as merely a thin dark
brown ring of crushed cells. There is no evidence of periderm formation.
The cortex is divided into an inner and outer zone of approximately equal thick-
ness. The inner part is composed of poorly preserved isodiametric thin-walled
cells containing numerous, scattered dark secrctory cells. The outer zone is thicker-
walled and usually better preserved, consisting of a compact tissue of brick-like
cells (hexagonal to circular in transverse section), about twice as long as wide, the
elongation being parallel to the axis of the stem. This merges into an outermost
tissue which is 2-3 cells thick and differentiated by being made up of cells four to
six times as long as broad. An unusual character of this tissue is the frequent
occurrence of multicellular emergences which are commonly broad at the base,
tapering to a sharp point. They are sometimes forked and horn-like (figs. 5 and
55) and may occur singly or in clusters (fig. 8). In length they average .6 mm.
There is no evidence that they were glandular like the emergences of Lyginopteris,
nor do they appear to have been arranged in parallel rows as has been described for
the latter genus (Scott, 1923). On the contrary, they are produced more or less
indiscriminately with the exception that they are nearly always present at the point
of departure of a branch.
A feature of the outer cortical zone which is probably the most unique in rela-
tion to the comparable pteridosperm genera is the presence of a vertical series of
horizonfally aligned sclerotic plates instead of the usual vertical strands. These
consist of thick-walled stone cells, 2-4 cells deep and 4-6 cells in diameter (fig.
10). In tangential section they are occasionally seen to anastomose with adjoining
plates at the same level and with plates above and below, thus appearing as a
loosely arranged horizontal network (fig. 11).
One of the most difficult problems in interpretation has been the question of
whether Microspermopteris bore leaves. As stated earlier, we have followed four
of the stems for approximately 6 cm., three for 4 cm., and another for about 1 cm.


1949]
BAXTER-FOSSIL PTERIDOSPERMS 293
This produced a close check on nearly 37 cm. of stem, all, of course, not of the
same plant. However in this rather respectable amount of material we encountered
only five instances of vascular tissue being given off from the main stele. In every
case the details are identical and are illustrated for both a young and mature speci-
men in figs. 1, 2, 3, 5 and 55.
The branch is first evident as a departure from the stele of a complete segment
of primary and secondary wood, with the crushed phloem and cambium tissues on
its outer, abaxial surface. At this point it consists of 8 to 12 metaxylem cells with
possibly 1 to 2 strands of protoxylem, bordered on the outer side by almost the
complete amount of secondary wood present at that particular point on the main
stele. This results in a conspicuous gap being produced in the mature stems and a
relatively smaller one in the young stems where the proportion of secondary growth
is much less. The angle of departure is acute (around 300), the trace following
this steep course through the cortex for approximately 2 to 3 mm. During this
space the secondary wood and enclosing parenchyma tissues completely surround
the primary core and produce a concentric bundle identical to the main stele except
in size. The bundle then turns sharply outwards and proceeds at right angles to
the stem axis for a distance approximately equal to the normal diameter of the
stem before again resuming an upward course. As shown in fig. 5, the branch,
where it projects horizontally out from the stem, almost equals the stem in size
and exhibits all of its characteristic sclerotic plates and cortical zones. At no
time does the bundle show any tendency to subdivide further, while a transverse
section of one of the branches at a point around 4 mm. from the main stem shows
it initiating a further small branch of its own in the same plane as the primary
one. The branching was apparently distichous at relatively long intervals, so that
the habit was probably fairly close to the partial reconstruction shown in pl. 5.
Adventitious roots, which are primarily limited to the axis of the branches, are
similar to those of Lyginopteris. They are commonly hexarch or heptarch with
conspicuous protoxylem groups at the points of the projecting arms (fig. 4). The
phloem lies between these arms and, as in Kaloxylon, there is a small amount of
conjunctive parenchyma in the metaxylem. The stele is enclosed by a single poorly
preserved dark ring which probably represents the endodermis. The cortex is
homogeneous and identical to the inner cortical zone of the stem. The peripheral
zone is undifferentiated, so that in transverse section the loosely packed cortical
tissue with scattered secretory cells appears to extend clear to the edge of the ir-
regularly lobed outer margin. This lack of a differentiated epidermal zone is one
of the distinguishing features between these roots and those of Lyginopteris.1
Secondary growth is rather rare but when present is again similar to that of
Kaloxylon, cambial activity initiating in the depressions between the protoxylem
1While the information in the literature is often vague on this point, similar roots have also been
described for Heterangiumin, although they are usually listed as diarch or triarch (Scott, 1923).


[VOL. 36
294 ANNALS OF THE MISSOURI BOTANICAL GARDEN
points and producing wedges of typical secondary wood alternating with wedge-
shaped rays opposite the protoxylem. The pitting is identical to that of the cor-
responding tissues in the stem. As might be expected, the roots are of constant
small size, with the most mature specimens showing 6-7 layers of secondary growth
not excecding 2 mm. in total diameter. The point of their insertion on the stem
offers another similarity to Kaloxylon as roots are most frequently found im-
mediately above the branch attachment (see Scott, 1923, p. 49) where their hori-
zontally departing bundle seems to function, in part, in filling up the branch gap.
As it has been possible to follow these roots from their insertion on the stem (fig. 6)
out to typical transverse sections as in fig. 56, their identity is beyond doubt.
Discussion:
At first glance, in transverse view Microspermopteris presents a close resem-
blance to Heterangium. The size is comparable to H. minimum (Scott, 1917),
and the primary wood with its thin network of parenchyma separating large groups
of tracheids is more closely approximated by H. Kukuki (Hirmer, 1933) although
the total amount of parenchyma is much less in Microspermopteris. In the anatomy
and insertion of the roots and the presence of multicellular emergences on the stem
and branches we have structures comparable to Lyginoptcris. However, the almost
solid protostele contrasts with that of Lyginopteris, while the absence of leaf traces
and of a vertical fibrous hypoderma, along with the exarch position of the proto-
xylem, removes all possibility of assigning the specimens to Heterangium.
While the horizon of our petrifactions is late Upper Carboniferous and H.
Grievii Scott is of Lower Carboniferous age, there seems little doubt but that we
are dealing with a more primitive plant which possibly represents the ancestral
stock of Heterangium. In fact, if it were possible to increase slightly the amount
of parenchyma in the primary wood, fuse (through webbing) the closely grouped
parallel branches into a multi-bundle rachis (Lignier's (1908) theory of mega-
phyllous development), and add a hypodermal zone of vertically elongated fiber
bands we would have a stem quite similar to Heterangium. The sclerotic plates
lying in the extreme outer cortical zone of Microspermopteris (fig. 10) are in radial
view somewhat similar to the plates found in the middle cortex of all of the
Heterangium species (with the exception of H. minimum which, according to
Scott, lacks fibrous and sclerotic tissue altogether).
The most obviously primitive and unusual feature, the leafless condition, can be
assumed to be demonstrated since our material permitted examination of approxi-
mately 37 cm. of different stems. The only similar character in plants of possible
pteridosperm affinities is in Eos permopteris (Aneurophyton) of the middle
Devonian.1 We must assume, then, partly on the lack of any intervening evidence,
that we are dealing with a link leading the pteridosperm complex clear back to the
1Although the fructifications originally described as seeds were later shown to be sporangia the
anatomy of the stem still provides some basis for including the genus in the pteridosperms.


1949]
BAXTER-FOSSIL PTERIDOSPERMS 295
Psilophytales. Indeed, Dawson's restoration of Psilophyton princeps (known only
from compressions) is disturbingly similar to our own restoration of Microsperm-
opteris, particularly in the flattened branching pattern and the presence of spine-like
emergences on the stem. Since what we know of Psilophyton stelar structure in-
dicates that it possessed only spiral and scalariform pitting there obviously cannot
be any direct comparison in internal anatomy with that of the secondary wood
and highly developed bordered pitting of Microspermopteris. However, the gross
appearance is close enough to intimate that a compression form of M. aphyllum
might be identified as a Psilophyton. The middle Devonian genus Schizopodium
offers a closer parallel in pitting and beginning of secondary growth. However,
we consider it here just an example of the early, contemporaneous origin of these
characters in contrast to the more conventionally primitive scalariform pits and
solitary primary tissues, since the present evidence indicates its relationship to the
Cladoxylaceae rather than the Pteridospermae.
In Andrews' (1940) account of the stelar anatomy of the pteridosperms he
makes the following observation:
. . it should be stated that the view that the pteridosperms represent an intermediate
group between the ferns and cycads is no longer tenable. Rather we must look to a common
psilophytalean-like ancestor with terminally borne sporangia, a solid protostele and primitive
secondary wood for the origin of the ferns and pteridosperms . . .
While we are more inclined to feel that the ferns arose independently, in many
ways our present genus fulfils the theoretical requirements outlined.
The possibility that M. aphyllum was parasitic and its leafless condition a
result of degeneracy rather than primitiveness has not been overlooked. The fact
that the habit was probably epiphytic (climbing) or prostrate in a swamp humus
tends to lend some weight to such a view as does the apparent absence of stomata
and potential photosynthetic tissues. However, since no organs resembling
haustoria are present and the roots resemble so closely the aerial ones of Lyginop-
teris we cannot consider a parasitic condition too seriously. At the saine time the
combination of so many characters common to both Lyginopteris and Heteranghim,
along with the more primitive stelar structure and lack of differentiation into
rachis and lamina, seems to point rather definitely to an ancestral form from which
both genera may have developed independently. This conflicts with Scott's (1923)
theory of Lyginopteris arising from a developmental series through the subgenus
Lyginangium, and it may be necessary to reconsider some of Kubart's transitional
Heterangiun species as being actually primitive Lyginopteris species leading back
to Microspermopteris.
Since no seeds or any fertile parts whatever have been found, it is necessary
to include Microspermoptcris among the numerous other organ genera assigned to
the seed-ferns on purely anatomical characters. It may be open to question whether
in its leafless condition it could have borne seeds. If they were present they were


[VOL. 36
296 ANNALS OF THE MISSOURI BOTANICAL GARDEN
more than likely terminal on the smallest branch divisions. However, there is no
reason for not considering the possibility that the stem anatomy constituting the
organ genera of pteridosperms did not precede the development of seeds (i.e.
Eospermopteris (Aneurophyton). Certainly in many of the Devonian and Lower
Carboniferous Calamopityaceae the presence of seeds is still to be proven, although
the degrce of differentiation into stem and leaf-bearing organs had obviously reached
a more advanced stage than that shown by Micros permopteris.
It can be hypothesized that certain small psilophytalian plants struggling for
survival in an environment of increasing lushness and density might well have
developed a vine-like habit, involving additional conductive stelar tissue as well as
supporting sclerotic and fibrous zones, to be followed chronologically by differen-
tiation into leaves (as a more efficient light-catching mechanism) and still later
by seeds as a product of the changing and possibly drying environment. Viewing
evolutionary change as a response to environmental change, it is difficult to see
seed production ever replacing reproduction by spores if there had not been a
constant impetus to survival under conditions unfavorable (lack of proper
moisture) to spore germination. It also seems likely that the struggle for living
space and light preceded the above conditions.
From the original psilophytalian stock larger and anatomically more complex
forms would arise independently, leading by gradual ecological adaptations to the
recognized groups of Carboniferous plants. Certainly, the contemperaneous asso-
ciation, even as early as the Upper Devonian period, of widely differing stelar
structures for the ferns and pteridosperms would seem to indicate that they had a
separate individual origin. Some of the earliest known forms assigned to the ferns
such as Arachnoxylon and Reimannia of the Upper-Middle Devonian show definite
affinities to the Carboniferous Zygopteroideae, while Eospermoptcris of about the
sanie age shows many seed-fern characters in spitc of apparently producing only
spores. Thus, although the picture is complicated by the existence of numerous
genera from compressions of which we have no knowledge of the internal anatomy
(i.e. Archeoptcris, etc.), the safest and most consistent distinction between the two
groups would seem to be stelar structure. Using this as a criterion, it would be
possible to have a phylogenetically correct classification including, on the one side,
pteridosperms, having only terminal sporangia and, on the other side, ferns ex-
hibiting heterospory. There certainly can be no reasonable objection to recognizing
that the seed-ferns must have passed through a sporangiate stage or that ferns may
not have achieved heterospory as a terminal development rather than as a stage in
seed production.
The designation of the group as Pteridospermae becomes increasingly unfor-
tunate if we recognize their independent origin from the Psilophytales and the fact
that the most primitive genera undoubtedly lacked seeds. The sanie situation has


1949]
BAXTER-FOSSIL PTERIDOSPERMS 297
been dealt with in the Lepidodendrales (i.e. Lepidocarpon vs. Lepidostrobus) with
much less confusion. Here the general plant structure and anatomy have been
accepted as the basis for the order, while seed production has been recognized as an
advanced stage of heterospory within certain species and genera. For some reason it
has never seemed necessary to create the Lycopsidospermae to include Lepidocarpon
although considered on the same basis as the pteridosperms such should be the case.
The following seem to the author to be the important points to bear in mind
in relation to Pteridospermae in question.
(1). They are psilophytalian in origin rather than arising from the ferns.
(2). They are possibly of dual origin, with Eospermopteris leading to the
Calamopityaceae complex and Microspermopteris leading to the Lyginopteris and
Medullosa complex.
(3). Leaves when present are large and fern-like; seeds when present are
basically terminal.
(4). The stem and petiole anatomy is constant and characteristic enough to
delimit clearly the group irrespective of known possession of seeds.
(5). Included on the basis of the above anatomical criteria are genera such as
Microspermopteris, which may or may not have had seeds, and Eospermopteris, in
which the possession of seeds seems doubtful.
(6). While genera known only from compressions such as Archeopteris may
be links in the pteridosperm chain, they are just as likely, in the absence of anatom-
ical evidence, to be true ferns. Heterospory, as shown by the modern genera
Salvinia and Marsilia, as well as the fossil lycopods, does not necessarily always
imply later seed development.
(7). Seed development in the pteridosperms may in some isolated cases have
preceded the differentiation of fern-like leaves with the seeds being borne terminally
on naked branches. In other words, we are possibly dealing with early seed-plants
which through parallel evolution developed fern-like leaves rather than, as orig-
inally thought, with ferns which developed seeds. The distinction may seem trivial,
but while the original premises are close the phylogenetic conclusions (depending
on which starting point is selected) are quite distinct. The terminal position of
the seed in Lyginopteris oldhamia and Aneimites fertilis are cases in point since
these species are among the oldest forms in which seeds are known.1 (We can only
hope that the discovery of fertile material of Microspermopteris will illuminate
this point.)
Diagnosis:
Stems of constant small size, the stele never exceeding 2.5 mm. or the entire
stem 5 mm. Metaxylcm of large cells (150 pi diameter), diminishing towards the
1 While these seeds are "terminal" on leafy fronds rather than on naked stems it seems not
unlikely that their apical position involves a carry-over from a developmental stage prior to the
acquisition of leaves.


[VOL. 36
298 ANNALS OF THE MISSOURI BOTANICAL GARDEN
periphery. Protoxylem exarch, of numerous indistinct groups. Xylem parenchyma
arranged in a thin network enclosing groups of 12 to 14 metaxylem cells. Sec-
ondary wood of small angular (in cross-section) tracheids from 3 to 16 layers in
thickness, increasing in size towards the outer edge. Reticulate-bordered pitting
with crossed orifices in the metaxylem and on radial walls of the secondary wood.
Scattered bordered pits with lineal openings on tangential walls. Protoxylem spiral
or annular. Rays rare or lacking; when present, small, uniscriate, 1-4 cells high.
Cortex differentiated into inner and outer zones. The inner zone composed of
isodiametric thin-walled cells, poorly preserved, with scattered secretory cells but
lacking sclerotic tissue. Outer zone of thicker-walled, longer cells containing
vertical series of horizontal sclerotic plates. Epidermis of similar but more elon-
gated cells producing numerous multicellular pointed emergences. Leaf traces
lacking. Branching distichous and at right angles to the stem. Roots adventitious,
hexarch to heptarch, commonly inserted above point of branch departure.
Horizon: Des Moines Series of Pennsylvanian.
Type: fig. 1. Slide 1602 in the paleobotanical collection of the Henry Shaw
School of Botany of Washington University.
SOME NEW AMERICAN MEDULLOSAS
In the interval since Thiessen (1920a, 1920b) discovered and identified a
pteridosperm stem as M. anglica (later to be assigned varietal distinction by Schopf,
1939) three new species and one variety of Medullosa from American coal balls
have been brought to light. They are: M. Noci (Steidtmann, 1937), M. distelica
(Schopf, 1939), M. Thompsonii (Andrews, 1945), and M. anglica var. ioensis
(Andrews & Kernen, 1946). With the exception of M. Noci all of these new
species and varicties have formed a fairly closely integrated group assignable to the
subgenus Anglorota along with the European species M. anjlica, M. centrofilis, and
M. npusilla. M. Nori, showing affinities with M. Leuckarti, is held to be transitional
between the Carboniferous form cycle and the Permian species.
Our knowledge of this very interesting group has been expanding rather rapidly,
and with the hope of throwing still further light on the subject three new species
of Medullosa are herewith described and additional new data are presented on
M. Noci.
Medullosa primaeva, sp. nov.:
The following description is based on a single coal ball specimen from the
Urbandale Mine located 1.2 miles west of Des Moines, Iowa, on U. S. Highway
No. 6. This is the same location from which Andrews (1945) described M.
Thompsonii. The horizon is the Des Moines Series of the Pennsylvanian. The
material was collected and cut by Mr. Frederick O. Thompson of Des Moines, who
generously donated it to the Henry Shaw School of Botany of Washington Uni-
versity. It consists of a cut block 5.5 x 5.5 cm. and 1.3 cm. thick, with the stem


19491
BAXTER-FOSSIL PTERIDOSPERMS 299
exposed on one side through a fracturing away of the adjoining material. The
stem's course is through the thickness of the block at a slight angle from the verti-
cal, the total available length being 1.4 cm. Figures 14 and 15 show the appear-
ance of the top and bottom surfaces of the specimen prior to any grinding of the
fractured edge. Approximately one half of the cortex and external tissues have
been lost on the side of the fracture, though the multiple stele appears to be nearly
intact.
As shown in fig. 14, the upper' surface of M. primaeva exhibits 5 rather large
and uniform-sized steles, 2 of them partially fused. There are also 2 small steles and
a portion of a third on the fractured margin. The lower surface shows the same 8
steles, though somewhat altered in orientation and size, with 3 of the steles partially
fused. It is not implied, however, that 8 was the constant number of steles as
even in the short length of stem available stelar fusions and divisions were num-
erous and the diversity of vascular growth even included the production of steles
running horizontally through the stem for short distances (fig. 13). Still, even
with these variations the stele number seems to have been constantly 6 or more.
The stem measures 2.0 cm. in diameter, the individual steles ranging from
around 5 mm. for the average large ones to .5 mm. for the very smallest. The 5
largest steles are closely comparable in size to those of M. Thompsonii even though
the stem of the latter is considerably larger, averaging 3.5 cm. in diameter. The
steles are essentially radially symmetrical with a very slight tendency towards
endocentricity.
It may be argued that some of the smaller vascular strands (fig. 14, S3 and S8)
do not constitute true steles. However, even the smallest possesses 8 or more
layers of secondary wood and can be seen to be independent in its course through-
out the entire length of the specimen (fig. 13). Neither can they be designated
as accessory strands from which leaf traces might be produced (as in Sutcliffia and
M. anglica) since the two largest of the 8 steles are, in our specimens, the sole
observed source of trace departure.
The primary wood is small in amount and is characterized by the almost com-
plete absence of parenchyma; what little there is being restricted to a thin network
running through or enclosing the primary cylinder, from which the high uniseriate
rays extend out through the secondary wood. The primary wood forms a cylin-
drical to irregularly shaped core around which it is often difficult to determine the
exact inner limits of secondary growth. The protoxylem is not distinguishable
(figs. 14 and 19).
The secondary wood is variable as to cell size and radial growth, the first-
formed layers being often composed of large tracheids (similar in size to the
metaxylem) which merge some distance out into rows of much smaller cells. On
I�Thc interpretation as to lower and upper surfaces of the stem is made on the basis of the
outward passage of leaf traces exposed in a series of longitudinal peels.


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300
ANNALS OF THE MISSOURI BOTANICAL GARDEN
the other hand, the same stele may, on the opposite side, show the first-formed
secondary wood to consist of very small (in diameter) tracheids and the successive
outermost cells to be large (fig. 19).
Each stele is enclosed by a dark tissue of crushed cells, probably of cambium
and phloem, in which are occasional small resin canals. The entire stelar assembly
is surrounded by a very thin, parenchymatous "periderm" which is never over 2 to
3 cells thick and is often so poorly preserved as to be indistinguishable from the
cortex.
The rays are up to 1 cm. or more in height and apparently constantly uniseriate.
In this regard they probably corne closest to Andrews' (1940) classification II B
in which he originally placed all of the Anglorota group as well as M. Noci and
M. Leuckarti.
The cortex is composed of cells rounded in transverse view but elongated
vertically two to three times their width. Traversing upward and outward through
the cortex are numerous small collateral leaf traces consisting solely of 3-4 proto-
xylem tracheids with spiral thickening (fig. 27) and an abaxial phloem group.
There is definitely no secondary wood associated with the trace. Mucilage canals
with their "resin rodlets" are scattered sparingly through the cortex and are un-
usually small, having a constant diameter of less than 60 jp. They are commonly
closely associated with the leaf traces and, in contrast to the majority of the other
American species, seem to have seldom invaded the hypodermal, sclerotic strand
zone.
The sclerotic strands form a single layer and in transverse view appear circular
to slightly radially elongated. They are separated by 2-3 layers of cortical-like
cells from a conspicuously darkened epidermis. This latter tissue consists of brick-
shaped cells with a slight tangental elongation and rather thick walls which oc-
casionally show evidences of a cuticle.
Discussion:
Our specimen shows a rather close similarity to Meduillosa Thompsonii in the
secretory canals-their small size, their comparative scarcity in the stem as a whole,
and their almost complete absence in the sclerotic fibrous zone. However, although
Andrews (1945) points out that the number of steles in the Medullosae is generally
an unreliable taxonomic character (stelar divisions and fusions often resulting in
variations of 2-3 or more steles), the possession by Medillosa primaeva of 7 to 8
steles, which tend to pursue horizontal courses through the stem and almost com-
pletely lack conjunctive primary parenchyma, clearly makes it of specific im-
portance and distinct from M. Thompsonii.
Medullosa centrofilis and M. pusilla are the only other species which seem similar
enough to deserve consideration. The former comes closest to M. primaeva in
number of steles (considering the "star ring" as a fourth stele) but lacks the hori-
zontal stelar meanderings and exhibits many more and larger secretory canals. M.


1949]
BAXTER-FOSSIL PTERIDOSPERMS 3UI
pusilla is comparable in over-all stem size but again is separated by the stele num-
ber, the difference between 3 and 7-8 being held as more than specific variation.
The slight tendency toward endocentricity of the secondary wood and paucity
of conjunctive parenchyma in the primary area, along with its generally netted
arrangement, make the individual steles more closely comparable to those of
Microspermopteris than to Heterangium. According to Bower's (1930) "size and
form" principles one would expect relatively little parenchyma in steles of such
small size, but comparison with the equally small stele of M. Thompsonii seems to
show greater differences than can be accounted for on the basis of Bower's hypoth-
esis. Thus although the M. primaeva stelar number is much larger than in any of
the other species of equivalent age the general stele structure appears to be more
primitive. This is in contrast to what might be considered advanced development
as evidenced by the absence of secondary wood in the leaf traces and leads one
to believe that the presence of such secondary wood in M. anglica is not necessarily
indicative of a primitiveness either for the character or the species as a whole. On
the contrary, it seems most logical at present to consider M. primaeva with its
numerous small, radially symmetrical steles as having developed from a monostelic
stem through stelar proliferation and accordingly representing a primitive stage
of the genus.
The specific name primaeva has therefore been assigned.
Diagnosis:
Stem small, not exceeding 3 cm. Steles numerous, 6-8, frequently fusing and
dividing, ranging from .5 to 5 mm. in diameter, often pursuing a sinuous hori-
zontal course through the stem. Primary wood parenchyma small in amount or
lacking. Resin canals small and few, almost entirely absent from fibrous hypo-
dermal zone. Rays uniseriate; secondary wood of variable cell size; irregular radial
growth, only slightly endocentric.
Horizon: Des Moines Series, Pennsylvanian.
Type: Fig. 14. Slide 1615 in the paleobotanical collections of the Henry Shaw
School of Botany of Washington University.
Medullosa elongata, sp. nov.
The following description is also based on coal-ball material collected by Mr.
F. O. Thompson and his associates of Des Moines, Iowa. The source was a large
open pit mine of the Atlas Coal Co. located in Wilson County, Iowa. The horizon
is Pennsylvanian, Des Moines Series.
The greater part of material from this locality was too heavily pyritized to
permit good plant preservation, but the stem fragments which were identifiable
indicate a flora consisting primarily of Lepidodendron and Calamites. Pteridosperms
were relatively rare, the present description being based on a single stem specimen
7 cm. long and 6 x 1.5 cm. in diameter. There evidently had been some crushing,
which would account partially, but not altogether, for the asymmetry (fig. 16).


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302 ANNALS OF THE MISSOURI BOTANICAL GARDEN
The outstanding feature of the three steles is their extreme endocentricity in
which character they resemble Schopf's (1939) M. distelica. The steles maintain
their individuality, i.e., no stelar fusion, and relative position throughout the 7 cm.
of stem length with the endocentric secondary development also showing a con-
stant approximate 4 to 1 ratio in thickness as compared to the exocentric secondary
tissues. The three steles are of equal size, averaging 10 X 2 mm., the plane of
elongation following that of the stem as a whole and constituting a factor in the
evidence that the general asymmetry was a natural character of the living plant.
Two of the steles occupy a position directly opposite one another and near the
center of the stem while the third is isolated off to one side (fig. 17). The primary
xylem consists of a long narrow area following the elongation of the stele. It is
seldom over 2 cells in width and runs up to 8 mm. in length. The metaxylem
tracheids are large (.2 mm.), and usually triangular in cross-section. There is
relatively little conjunctive parenchyma, while the protoxylem is indiscernible.
The secondary wood is rather unusual for a Medullosa in that the majority of
the cells are square in transverse view, while the others are of the more character-
istic alternately arranged pentagonal shape. Also, in contrast to the somewhat
similar M. distelica, the radial rows of secondary tracheids are not conspicuously
divided by rays nor are the outermost cells differentiated. In addition, the rays are
uniseriate, not particularly numerous, and almost impossible to detect in transverse
view.
Surrounding each stele is a thin dark layer of crushed cells containing numerous
small resin canals. The periderm is thin (3-4 cells), poorly preserved, and ap-
parently interrupted at the narrow ends of the steles where the leaf traces are given
off. The cortex is rather poorly preserved due to pyritization, with numerous
rather large slime canals (.2 mm. in diameter) scattered throughout it and also
conspicuously associated with the fiber strands in the sclerotic-fiber hypodermal
zone. The fiber strands are arranged in 2-3 alternating rows, the individual strands
being somewhat radially elongated. A rather striking character of the species is
the large "compound" resin canals running horizontally through the stem. They
measure 1.3 mm. in diameter and are approximately six times the size of the
vertical canals. Figure 18 illustrates several of these canals at the same magni-
fication as the vertical canals in fig. 17. They are lined with numerous small
triangular and diamond-shaped secretory cells which appear to contain the same
black resin substance as the canal itself.
The leaf traces are given off from the narrow ends of the flattened steles and
are initially quite large, consisting of 10-12 or more primary tracheids which
divide farther out in the leaf bases into numerous smaller bundles. Three leaf
bases are shown in fig. 16, two detaching themselves from the narrow transverse
extremities of the stem and approximately parallel to it, while the third is being
given off from the stem's broad side and at right angles to it. Thus it would ap-
pear that in M. elongata we are dealing with a creeping stem of possibly dorsi-


1949]
BAXTER-FOSSIL PTERIDOSPERMS _30
ventral symmetry. As stated earlier, the dimensions of 6 X 1.5 cm. for the stem
can be only slightly attributable to crushing while the equivalent asymmetry of
the steles and general lack of any crushed tissue indicate the form to be more or
less characteristic of the living plant. In addition, the 7 cm. of stem length of our
specimen exhibits rather short internodes, with several leaf bases given off in the
same bilateral plane from the narrow opposite stem sides.
The position of the stem on the edge of the containing coal ball prevented
observation of more than the one dorsal leaf base shown in fig. 16. However, it
seems plausible that these erect leaves were produced between internodes as short
as the lateral ones.
As implied previously, M. elongata is most closely comparable to M. distelica on
the basis of the extreme endocentric secondary growth. However, in the possession
of three steles, which at no time show any tendency towards fusion, the difference
in primary wood, fewer and uniseriate rays, and square secondary tracheids, as well
as the large compound resin canals and apparent dorsi-ventral habit, M. elongata
is clearly distinct and of specific importance.
The species name elongata is assigned in recognition of the asymmetric trans-
verse elongation of the steles (10 X 2 mm.), as well as the equivalent transverse
elongation of the stem as a whole.
Diagnosis:
Stem asymmetric to bilaterally symmetric, approximately 6 X 1.5 cm. in diam-
eter, only slightly crushed in the smaller dimensions. Steles 3, extremely endo-
centric, 2 opposite one another in stem center, the third isolated to one side, retain-
ing their relative positions and not fusing or dividing in over 7 cm. of stem length.
Vertical resin canals numerous, averaging .2 cm. in diameter; fewer horizontal,
large compound resin canals averaging 1.3 cm. in diameter. Habit creeping or
climbing with leaves being given off from sides and dorsal surface of stem.
Locality: Atlas strip mine, Wilson County, Iowa.
Horizon: Pennsylvanian, Des Moines Series.
Type Specimen: Fig. 16. Slide 1617, in the paleobotanical collections of the
Henry Shaw School of Botany of Washington University.
Medullosa endocentrica, sp. nov.:
This third new medullosan stem comes from coal-ball material found in a
stream bed outcropping near Berryville, Illinois. The location is near to that from
which Steidtmann (1937) described M. Noei, and the horizon is the same, being
determined as the upper part of the McLeansboro group of the Pennsylvanian of
Illinois. The coal ball containing the specimen was 15 cm. long by 8 cm. wide.
The stem followed a straight course through almost the complete longer axis, being
itself 12 cm. long and 1.2 X .7 cm. in diameter. These dimensions are of the
stelar system only, the cortex and other external tissues having been lost. How-
ever, as can be seen by referring to fig. 20, the unique appearance of the steles seems


[VOL. 36
ANNALS OF THE MISSOURI BOTANICAL GARDEN
to justify recognizing the specimen as a new species and possible culmination of
endocentric development, in spite of the lack of information as to the stem's
external anatomy.
The stem consists of 3 steles, 2 of which are 5 X 5 mm. in diameter, the third,
2 X 1.5 mm. in diameter, situated on the side equidistant between them. Sec-
ondary growth is almost entirely endocentric, only one of the larger steles showing
a very small amount of exocentric growth. These characters are constant for the
entire 12 cm. of stem length as are also the relative stelar positions. Thus there
can be little doubt that this extreme centripetal growth was a distinct feature of
the living plant, and the evidence also suggests that the stelar system had achieved
a degree of uniformity not found in any of the other Anglorota species.
The primary area of each stele is oval in transverse view, and measures 1.5 X 1
mm. in the 2 larger steles. It consists of scattered groups of large metaxylem cells
intermixed with considerable conjunctive parenchyma. The protoxylem appears
to consist of two small exarch groups of tracheids with annular thickening while
the metaxylem shows the characteristic dense reticulate bordered pitting.
The secondary growth is produced in a fan-like pattern, radiating towards the
stem center for an average of 15 cells in the large steles and 6 cells in the small
stele. The transverse dimension of the cells increases gradually from the innermost
to the outer rows but on the average is quite large, around .2 mm. The rays are of
great height, more than 1.7 cm., and in the wood are uniseriate or at the most 2
cells wide. They commonly separate radial rows of 2-3 tracheids (fig. 22).
The pitting of the secondary wood is bordered and densely reticulate on the
radial and oblique-tangential walls, with relatively few scattered pits on the directly
tangential surfaces. The length of the individual tracheids is also quite extreme,
an almost perfect tangential section showing them to be over 1.7 cm. Adjoining
the outermost secondary wood (and continuous with it in general pattern and ray
position) is a rather disorganized tissue which we were at first inclined to interpret
as undifferentiated secondary wood. It consists of large thin-walled cells, similar
in size and shape to the secondary tracheids but completely unpitted. On entering
this zone the thin rays of the wood become greatly expanded, averaging from 4 to
8 or more cells in width, and appearing to be completely mature in their develop-
ment (fig. 21). This point, along with the total absence of any rudimentary pitting,
in cither the tangential or radial walls of the vertical elements, in our opinion, makes
it very unlikely that the cells are immature secondary tracheids. On the other
hand, one or two of our tangential peels through this zone shows vestiges of what
appear to be disarranged transverse walls with extremely small pores similar to the
sieve plates of living plants (fig. 23). Scott, in his description of M. anglica, has
pointed out that the rays become much wider in the phloem zone, while excep-
tionally large sieve tubes are common to plants of vine-like habit. Therefore, on
the basis of the above evidence (which may be not entirely conclusive), along
with the position of the tissue, we are inclined to consider it tentatively as phloem-
like in nature.
304


1949]
BAXTER-FOSSIL PTERIDOSPERMS 30U>
Lying between this phloem region of the three steles is a thin parenchymatous
zone of vertically elongated cells in which are scattered numerous resin canals con-
taining their opaque resin rodlets. The entire stelar assembly is completely sur-
rounded by a thin layer of dark, crushed cells of possible periderm nature.
The specific name endocentrica is assigned on the basis of the complete and
constant centripetal secondary growth.
Diagnosis:
Steles small, not exceeding 5 X 5 mm., 2 opposite one another and of equal
size, the third smaller, situated on the side between them. Secondary growth
completely centripetal. Primary xylem exarch. Metaxylem with considerable
conjunctive parenchyma. Rays 1-2 cells wide, expanding in the conspicuous phloem
zone to 4-8 cells in width, exceeding 1.5 cm. in height.
Horizon: Upper part of the McLeansboro group, Pennsylvanian of Illinois.
Type: Fig. 20. Slide 1619 in the paleobotanical collections of the Henry Shaw
School of Botany of Washington University.
Discussion:
As stated previously, Medullosa endocentrica appears to represent the ultimate
in centripetal secondary development, and accordingly its closest affinities lie in
the direction of M. distelica and M. elongata. It differs from the former primarily
in possessing a third distinct small stele, constant for the whole stem and in the
more perfect symmetry of the opposing "twin" steles. It differs from M. clongata
in stele shape (M. elongata averaging 10 X 2 mm.), as well as in the character
of the primary wood and amount of conjunctive parenchyma. M. endocentrica
differs from ail the other Medullosas in its constant degree of endocentricity and
the possession of a unique phloem zone of exceptionally large sieve tubes.
It is possibly significant that here, as in M. elongata, we appear to be dealing
with a stem of more bilateral (dorsi-ventral) than radial symmetry. From the form
of stele development in M. endocentrica (fig. 20) leaf traces could only have been
given off in the three planes opposite the abaxial sides of the primary xylem groups.
Thus while the orientation of the steles is somewhat different in the two species it
is likely that the phyllotaxy was similar, the leaves being produced laterally and
vertically (dorsally) with the side lacking a leaf trace source being considered
ventral.1 The predominance of 3 stele forms in the Medullosae is perhaps indicative
of this trend, which, however, reaches its inescapable climax only in the extremely
endocentric species. M. endocentrica has apparently almost reached the limit of its
potential stem enlargement through secondary growth but it is still much too small
to permit interpretation as an arborescent plant. Therefore it could not possibly
lit should be pointed out here that since the traces show no evidence of "girdling," the direction
of their initial departure is a valid indication of the stem's phyllotaxy.


[VOL. 36
306 ANNALS OF THE MISSOURI BOTANICAL GARDEN
have attained a habit comparable to that suggested in the reconstruction of M.
Thompsonii (Andrews, 1945). Also if it produced relatively large Alethopteris-
type fronds, as appears likely from the numerous associated leaves, it must have
been a prostrate or climbing vine since the small stem would be incapable of sup-
porting any such great weight. Thus the line of endocentric development from M.
distelica and M. elongata to M. endocentrica appears to be one leading to constantly
diminishing size accompanied by a change from radial symmetry of the stem with
complete spiral phyllotaxy to a bilateral, dorsiventral symmetry with lateral and
dorsal leaves. Extreme asymmetry can accordingly be seen to be an advanced rather
than primitive character, which as it reached its climax resulted in a line of "dead-
end" development in which the stem size was small and fixed. In this viewpoint
we agree with Schopf (1939, page 204) where he states:
It seems more tenable to consider the distelar condition in the new Nashville Medullosa
as reduced from a more polystelar type rather than as directly derived from an ancestry
reminiscent of Sutcliffia. It is also apparent that the extreme endocentric asymmetry found
in M. distelica is not a primitive feature.
We have included in the above quotation Dr. Schopf's statement on a distelar
condition probably resulting from the fusion of a polystelar type in that it also
agrees with our conception of what seems to be another and more important line
of development in the Medullosas. As pointed out in the discussion of M. primaeva,
a polystelar condition with numerous small radially symmetrical steles would seem
to have arisen most logically by stelar proliferation of a monostelic stem with a
similar small symmetrical stele. Then through subsequent tendencies to stelar
fusion the line would lead through the small tetra- and tri-stelar forms to the
large asymmetric stelar forms such as M. anglica and M. Noei.
The fact that the smallest species (M. primaeva and M. pnsilla) have the most
radially symmetrical steles while the larger species (M. Thompsonii, M. elongata,
M. distelica and M. anglica) all have greatly elongated (transversely) asymmetric
steles is evidence, in our opinion, that the latter have been derived from polystelic
fusion. (A good example of this point is illustrated in Andrews' (1945) diagrams
of stelar fusion in M. Thompsonii where it can be seen that the fusion produces a
larger, more asymmetric and more endocentric stele). Where the fusion standard-
ized itself at 3 steles of approximately equal size, or with one slightly smaller, a
balance appears to have been reached which was only upset by the origin of the
erratic cambial growths of M. Noei.
Regarding the phyllotaxy of the predominately 3-steled forms it may also be
pointed out that while the leaf arrangement has been mainly interpreted as spiral,
Scott, in working with a specimen of M. anglica one foot in length, showed that
the leaves were still produced on only three sides of the stem (text-fig. 1). While
Scott himself did not enlarge on this evidence, it seems to imply (when correlated
with forms such as M. elongata and M. endocentrica) that the significance of the
normal number of 3 steles in the Carboniferous Medullosas lies in the essentially


1949]
BAXTER-FOSSIL PTERIDOSPERMS 307
dorsi-ventral habit of the plant as a whole. As may be noted in text-fig. 1 of M.
anglica (which is typical for most of the 3-stele species), the steles are arranged in
the shape of a flattened triangle, the obtuse apex being always towards the flattened
side of the stem from which the dorsal leaf bases are produced, while the steles at
the opposite acute angles are oriented towards the position of the lateral leaves.
Spd st sc
a b
Text-fig. 1. Medullosa anglica: o.c., outer cortex; 1.t., leaf trace; st, stele; pd, periderm;
se, sclerotic strands separating petiole from stem; r, root; an, accessory strand. A, B, C,
AB and BC represent the points of leaf departure with the phyllotaxy being 2/5. Note that
this arrangement still leates one side of the stem completely devoid of leaves; so that the
habit may be assumed to have been dorsi-ventral (after Scott).
This bilateral symmetry is borne out also in the over-all stem shape of nearly
all of the 3- to 4-steled group. M. centrofilis had a stem diameter of 5 X 1.5 cm.;
M. pusilla, 2.2 X 1.3 cm. (Scott points out that the larger diameter here had lost
considerable tissue and was probably still greater in life); M. Thompsonii, 7 X 2.5
cm.; M. anglica, 10.5 X 3.7 cm.; M. elongata, 6 X 1.5 cm. M. endocentrica also
undoubtedly had a flattened stem but the lack of preservation of the outer tissues
in our specimen precludes such measurements. Ail of the above figures include the
attached leaf bases, but since it has been shown that these were always decurrent
for long distances on the stem and more or less overlapped, the measurements give
a truer habit proportion than those of the stem alone would. The asymmetry can
be seen to be quite constant in a proportion of 3:1, which fact alone makes it ex-
tremely doubtful that it is altogether due to crushing. De Fraine states for M.
centrofilis that "the shape of the stem with its covering of leaf bases was thus
distinctly flattened."
It would seem that the dorsi-ventral habit, while most obvious in species
such as M. elongata and M. endocentrica was also the rule in the majority of the
other species. M. Thompsonii is a possible exception since rather careful study of
the type specimen seems to indicate that in this particular stem the orientation of
the stelar assembly tends to vary, so that the planes of leaf trace departure are dis-


[ VoL. 36
308 ANNALS OF THE MISSOURI BOTANICAL GARDEN
tributed more generally in the four opposing radii and thus supply petioles in a
true radially symmetrical spiral phyllotaxy. However, such variations are not too
unusual. Selaginella, for example, in the two present-day species, S. rupestris and
S. apoda, shows a variation from erect plants with radial symmetry to creeping
plants with bilateral symmetry. This view, accordingly, makes it necessary to
visualize the Medullosae as primarily an assemblage of creeping or climbing plants
rather than as comparable to present-day tree ferns. The prostrate habit has
previously been postulated by several earlier workers on the basis of the small stem
of the Anglorota plants, while the great stem length recorded by Weber and
Sterzel (1896) for some of the Permian specimens is almost conclusive proof of
the vine-like habit of the much younger species. Weber and Sterzel state:
Bei Stimmchen wie M 43, das bei 92 cm. Linge nur einen Durchmesser von durch-
schnittlich 8.8:4.4 cm. besitzt, k�nnte man wohl an die von G�ppert & Stenzel vermutete
Schlingpflanzennatur der Medullosen denken. . . . Die im Anhang sub I Seite 105 (64)
geschilderten Medullosenstammchen beweisen dass insbesondere Medullosa stcllata cin� schlank-
cylindrische Gestalt mit periodischen Anschwellungen des Holzkarpers und auch im Uebrigen
merklich wechselndem Durchmesscr haben k�nnte, so das man, wie schon erw3hnt, mit
G�ppert & Stenzel an Schlingpflanzen denken k�nnte. In dieser Form des Wachstums liegt
wohl auch das verhaltnismissig haufige Vorkommen von Bruchsticken dieser Art begrindet.
In addition to the evidence offered by the dorsi-ventral flattened stem, the
phyllotaxy, and the great stem length in relation to its width, there is also consider-
able anatomical proof that the Medullosae were primarily prostrate or climbing
vines. Solereder (1908) has shown that unequal xylem growth and flattened stems
are characteristic of many living lianas, while Westermaier and Ambronn (1881)
have pointed out that tracheids and sieve tubes of more than average diameter are
typical of living climbing plants. As noted by Andrews (1940), the tracheids of
M. Noei and M. anglica may reach a diameter of 250 f� (larger than most vessels)
while M. endocentrica has extremely broad sieve tubes.
Although the acquisition of concentric rings of exocentric secondary wood
permitted an increase in size of the Permian Medullosas, along with a possible return
to a radially symmetrical spiral phyllotaxy, the vine-like habit of their Carbo-
niferous predecessors appears to have been largely retained.
The absence of a vine-like habit in the living or fossil cycads need not present
any insurmountable difficulties in retaining the theories of their origin from the
Medullosas, since, with the increased girth afforded by centrifugal secondary growth,
the developmental trend may be assumed to have been away from climbing towards
arborescent forms. This change may also have been influenced and accompanied
by a disappearance from the scene of the potentially supporting Psaronius, Cala-
mites and Lepidodendron through a gradual shift to a xerophytic environment.
To summarize and restate our evidence:
1. A large number of small symmetrical steles with almost solid primary wood
represents the primitive condition. Of the different specimens which have so far


1949]
BAXTER-FOSSIL PTERIDOSPERMS
5utdliEli"a
AI.
309
L. ste/ata
/'
'.Leuvcfarti
/Ae
A,e/
A~'.ang1a I. d�isteii'ca
AI. e/o ngata
' 1. enc/ocentrica
/1. Ehomp.soniu
MI. ceetrofj/ s
N. primevay
PSiL-0H-TALE ' (Microspermopteris V
Text-fig. 2. Proposed Medullosa phyletic chart. Explanation in text.
been described, M. primaeva seems to most nearly represent this stage. In this light
it seems probable that the origin was not from Heterangium but rather from a
more ancient form possibly akin to Microspermopteris. Arnold (1940) has de-
scribed a small polystelic stem from the Middle Devonian of New York to which
he has given the name Xenocladia medullosina. It consists of 9-10 small (not
much over 1 mm.) steles with a small solid protostele. He states that: "Xeno-
cladia may eventually prove to be a representative of some intermediate stage be-
tween the Psilophytales and certain of the polystelic Pteridosperms." While we


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ANNALS OF THE MISSOURI BOTANICAL GARDEN
are not inclined to attach too much weight to any direct connection between Xeno-
cladia and a stem such as M. primaeva, it does show the possible origin of a poly-
stelic structure contemporaneous with Rihynia and Hornea and, along with Micro-
spermopteris, indicates a psilophytalian origin for the pteridosperms.
2. Through subsequent tendencies to fusion the stele number eventually be-
came standardized at 3, with occasional variations of 2 or 4 through further fusion
or division.
3. Accompanying the above transition there was an increase in the size of
the plants and conscquently of the leaves, which (since in a closely grouped poly-
stele the leaf traces of necessity are produced from the abaxial sides) tended to
inhibit exocentric (centrifugal) secondary growth and thus resulted in an endo-
centric (centripetal) asymmetry of the steles.
4. As this endocentricity became pronounced the production of leaf traces
also became more localized on the abaxial stelar sides, resulting in a phyllotaxy of
lateral and dorsal leaves (text-fig. 1, M. anglica). M. elongata and M. endo-
centrica represent a climax of this trend which in the latter undoubtedly formed
an end development.
5. Where the endocentricity did not reach such extremes, the plants tended
to increase in size through the production of accessory vascular strands (M.
anglica), while eventually tangential secondary growth (to compensate for the
limitations of endocentric growth), along with the origin of prolific erratic cambial
zones (M. Noci), led to the larger and more complex Permian species. Text-fig. 2
shows a provisional and tentative phyletic chart based on the above points. Al-
though the horizon of all of the American species is considerably higher than that
of the European ones, the evidence of the stems themselves still seems to justify the
reverse grouping. For the reasons given above M. primacva constitutes the base
with the main line of development leading through M. Noci and M. Leuckarti to
the Permian forms, while the three extremely endocentric species constitute a
dead-end side chain of development.
Medullosa anglica is placed near the top because of its relatively large size and
erratic "periderm" resembling that of M. Noci. The large leaf traces with sec-
ondary growth may be viewed as advanced and of the nature of specialized ac-
cessory vascular strands to supply the increased needs of the enlarged petioles. Also
Sutcliffia, differing from M. anglica primarily only in its monostelic structure, may
be regarded as resulting from a fusion of the threc steles.
Medullosa Noci Steidtmann:
Steidtmann (1937, 1944) established M. Noci as the first clearly recognizable
American species of the genus and gave us an excellent description of the salient
features and peculiarities of the stem as well as the associated leaves, roots, and
seeds. However, the holotype on which he based most of his description had only
310


19491
BAXTER-FOSSIL PTERIDOSPERMS 5 11
one stele with portions of two others, while our present specimen consists of a
nearly entire stem with three large complete steles. It was collected from the same
outcrop near Berryville, Illinois, that produced M. endocentrica and is exceptionally
well preserved in its cellular details. The coal ball, of which the stem constituted
almost the entire bulk, was 28.6 cm. long and approximately 16 X 7 cm. wide in
the middle portion, tapering to blunt points at either end.
The essential features offering possibilities of an enlarged interpretation and
understanding of the species are:
1. The presence of a distinctive phloem zone characterized by broadened ex-
tensions of the medullary rays.
2. "Periderm rings" which show a transitional development of secondary
wood, a stelar origin, and a remarkable similarity to the Permian Medullosac "star-
rings."
3. Adventious roots, which run for long distances through the cortex parallel
to the steles, range from triarch to pentarch, and show a well-preserved aerenchy-
matous cortex.
Before discussing these points in detail a brief description of the stem as a
whole will be given. As shown in text-fig. 3, there are three large steles, tan-
gentially elongated, which occupy the major portion of the area as seen in trans-
verse section. Throughout the 28.6 cm. of stem length they remain essentially
independent although steles a and c occasionally partially fuse and then re-separate.
Their orientation with relation to one another is similar to that of the steles in M.
elongata, two of the steles being side by side while the third occupies a position off
to one side. They average 6 X 1.5 cm. in diameter and show no particular endo-
centricity, the secondary growth being the greatest in a tangential plane rather
than towards the stem center. This is a greater elongation than was usual in
Steidtmann's specimen, although he records that the stele did at times reach a
measurement of 6 X 1.8 cm., which is certainly close to the above. For the rest,
the primary and secondary wood are essentially equivalent to Steidtmann's speci-
men and exhibit primary tracheal bundles, prolific and erratic "periderm" growths,
and tetrarch roots originating in and running through the primary area. The
cortex is crowded with "periderm" rings and tangentially elongated bands, as well
as with the numerous large adventitious roots with their many small branches.
The hypodermal sclerotic zone is present as the outermost limiting tissue, the leaf
bases being absent. While there are apparent general differences between the
present specimen and Steidtmann's diagnosis of M. Noci (mainly in the lack of
any pronounced endocentric growth, and absence of a definite broad periderm
zone), it is felt that the variations fall within those allowable to a species, partic-
ularlv in the Medullosas. The following descriptions of the previously outlined
characters are therefore intended solely as an addition to the M. Noei diagnosis and
not as of new specific or varietal importance.


[VOL. 36
ANNALS OF THE MISSOURI BOTANICAL GARDEN
Text-fig. 3. Medullosa Noci: a, b, and c indicate the three steles. PI and P2 are the
"periderm" or "cambial" rings. Ail of the other vascular strands represent adventitious
cortical roots. Additional explanation in the text. X 4/5.
It is understandable how a great deal of the M. Noei material might be ex-
amined without observing the striking phloem rays, since they are only occasionally
evident even in the exceptionally well-preserved present specimen, their place
being usually occupied by invasions of the prolific "periderm" tissue. However, as
shown in fig. 26 the rays with their dark brown secretory cells sometimes form a
quite prominent fringe around the stele. They vary from 1 to 2 mm. in length
(outside the wood) and from 4 to 8 cells in width, spreading out fan-like towards
their outer margin. The cells are radially elongated and contain numerous black
globules of evident secretory nature. The tissue lying between the rays is seldom
well preserved. Whatever sieve tubes that might have once existed are consistently
represented by disorganized cellular fragments. The general aspect as seen in
transverse section is rather similar to the expanded "phloem rays" of M. endo-
centrica, the rays in both species being characterized by their dark brown color and
black secretory cells, as well as in their greater width as compared to their structure
in the xylem.
As mentioned previously, numerous adventitious roots run through the cortex.
They vary from tetrarch ones, which apparently originate in and run through the
primary part of the stele for some distance before emerging, to triarch and
pentarch ones, which seem to arise in the "periderm" adjoining the stele and follow
a vertical course through the cortex for long distances before emerging. Some of
these cortical roots attain considerable size (up to 2 X 2.5 cm.) and are some-
times difficult to distinguish from small steles (text-fig. 3). They are often
beautifully preserved and show an aerenchymatous cortex, a feature strongly sug-
gestive of a moist or aquatic habitat (fig. 25).
312


1949]
BAXTER-FOSSIL PTERIDOSPERMS 313
It may be pointed out here that Worsdell (1906) has found that the Cycadaceae
show a similar variability in root anatomy with pentarch or tetrarch roots nor-
mally borne adventitiously near the base of the plant and the diarch and triarch
roots produced towards the apex.
In Steidtmann's (1937) preliminary report he stated that M. Noei apparently
had thrce large steles with at least two "star rings." Later, in his more intensive
and complete treatment of the species (1944), he indicated that the structures
which he had initially reported as "star rings" proved on closer observation to be
"large concentric strands of the ever-present periderm." Now, our present speci-
men seems to show that Steidtmann's first view was the correct one and that the
periderm or "cambial" rings possibly do represent developing "star rings."
De Fraine (1914) points out that the "star ring" of M. centrofilis differed from
the star rings of the Permian stems in that it was basically protostelic while the
latter, as implied by the constant reference to a "partialmark," were largely
parenchymatous. This distinction is shown in pl. 10, where not only the difference
between the M. centrofilis type of "star ring" and that of M. stellata is evident but
also the considerable similarity between the latter and an M. Noei "cambial ring."
Accordingly, the use of the term "star ring" for the fourth small stele in M. centro-
filis was probably ill-advised, as it obviously had little in common with the majority
of the structures so named in the Permian species but merely constituted a small
independent stele. On the other hand, the evidence seems clear that in M. Noei we
have, for the first time in a Carboniferous stem, the appearance of structures
equivalent to the Permian "star rings." The fact that it was not until after a
careful examination of his specimen that Steidtmann decided the structures were
too similar to the profuse erratic periderm growths to be called "star rings" sug-
gests that the "sternringen" of the poorly preserved, silicified stems of "des Rot-
liegenden von Chemnitz-Hilbersdorf" may also have been "periderm growths."
Certainly the observable detail of the Weber & Sterzel specimens was hardly com-
parable to that to be found in good coal-ball material.
Steidtmann (1944) discussed the advisability of using the term "periderm"
for these prolific growths, and came to the conclusion that it was valid since it did
not necessarily imply suberization. However, in our specimen it can be seen that
the tissue (at least that which forms many of the rings) originates in the primary
part of the stele, and, instead of being an invasion from the cortex, itself produces
outgrowths which occasionally penetrate the secondary wood and extrude into and
through the cortex. Figure 24 shows a ring from the primary area of stele a
(text-fig. 3) in which a certain amount of differentiation into secondary xylem
has taken place, indicating that the tissue was more of a true cambial nature than
periderm. That these "cambial rings," like some of the roots, originated within
the stele is clearly shown by their continuous vertical course throughout the stele
both above and below the occasional cortical invasions.


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314 ANNALS OF THE MISSOURI BOTANICAL GARDEN
There is also the new evidence which has corne to light in M. Tbompsonii that
the "star rings" may, in part, be derived from a congestion of leaf traces. Figure
59 shows a diagram of a portion of M. Thompsonii which has just given off a
petiole. The hypodermal fiber strands are lacking on the one side and the cortical
area containing the outgoing traces is considerably diminished. Arranged in a line
along the stem margin in this area are numerous thin-walled xylem "rings" with
a central core and radial secondary tissues (figs. 30 and 59). Successive peels,
downward through the stem, show that these "rings" result from a fusion of two
or more outgoing traces. It seems that the traces, while still being prolifically
formed, lacked an expanding cortical area in which to scatter out, and consequent-
ly became congested and fused with a subsequent production of secondary
growth. The limitations of the M. Thonipsonii material do not allow observation
of the final disposition of these "rings," but it seems likely, with the increase in
the cortical area on approaching the next node, that the "rings" or "aggregate"
traces may have redivided and lost their secondary wood.
If in the early ontogeny of the Permian Medullosas there were numerous leaf
traces produced towards the center of the stem, the same congestion and fusion
might possibly have resulted in the medullary "star rings" of M. Solmsii, with the
central position inhibiting subsequent redivision. We are inclined to follow Wors-
dell (1906) rather than DeFraine (1912) in that (as pointed out in the previous
discussion) we regard the Permian Medullosas as leading to the Cycads, with Sut-
cliffia as an advanced rather than primitive member of the Medullosae. The above
theory of a leaf trace origin for the "star rings" would offer further evidence for
Worsdell's view that the collateral rings of the Permian Medullosas and the Cycads
are "composed of the one-sided remnants of a number of steles," since only in such
a polystelar structure could the leaf traces be produced towards the center.
To pursue the conception still further, De Fraine (1912) states: "There ap-
pears to be no serious objection to the view that the 'meristeles' of Sulcliffia are
homologous with the leaf trace strands which leave the stele in M. anglica for botli
appear to be entirely used up in the formation of foliar bundles." Following the
same reasoning, the marginal vascular rings in M. Thompsonii may also be con-
sidered as homologous to the above in that they differ only in forming in the cortex
rather than at the stele margin, while the Permian "star rings" may also be
homologous except that they were not used up in the formation of foliar bundles
due to their internal position. Thus the extra-fascicular zones and accessory corti-
cal and pith strands (star rings) of Medullosa, Sutcliffia, and the present-day
Cycads are possibly ail equivalent in that they may represent aggregations of fused
leaf traces around which the secondary growth has become concentric producing
rings or (where adjoining groups become contiguous) forming collateral bands.


1949]
BAXTER-FOSSIL PTERIDOSPERMS 3 15
SOME MICROSPORANGIATE FRUCTIFICATIONS ASSIGNED TO THE MEDULLOSAE
The abundance and variety of Medullosa stem and petiole remains in the Iowa
and Illinois coal balls indicate clearly that the group was a dominant and wide-
spread feature of the Carboniferous flora. As Andrews (1948) points out: "The
wide range in anatomy exhibited by the Upper Carboniferous and Permian
medullosas almost certainiy represents an assemblage of familial or possibly ordinal
rank rather than simply a genus." Accordingly, it is not surprising to find a
corresponding diversity beginning to be evidenced among the other organ genera
usually associated with and regarded as belonging to the Medullosa stems. This is
particularly true of the interesting microsporangiate fructification known as
Dolerotheca. Dolerotheca is characterized by a large campanulum containing
radially arranged rows of paired tubular sporangia. The evidence for its being a
medullosan pollen-bearing organ is almost conclusive although it has not as yet
been found attached. Dr. J. M. Schopf (1948), in addition to describing three
new species from Illinois coal balls, has given a comprehensive historical, taxonomic,
and phylogenetic discussion of the genus and certain allied forms. Therefore we
shall limit ourselves here to describing briefly two additional new species of Dolero-
theca from coal-ball material collected at the What Cheer Clay Products Co. coal
mine, What Cheer, Iowa. This horizon is designated only as the Des Moines Series,
Pennsylvanian, but as we shall point out later may be tentatively assumed to be of
considerably greater age than the lowest Illinois horizon in which petrifactions of
Dolerotheca have been found.
Dolerotheca sclerotica, sp. nov.:
The general shape is that of a broad rather shallow campanulum approximately
25 mm. in diameter and 5-7 mm. deep (fig. 45). The epidermis of the proximal
sides is represented by a layer of tangentially elongated cells with conspicuous dark
contents, on which are scattered a few very small capitate glandular hairs (fig. 58).
Just within this layer is a definite sclerotic hypodermal zone, .4 mm. in thickness, of
empty isodiametric cells, only approximately 1 out of 30 showing a black secretory
plug (fig. 49). Lying immediately inside this latter zone is the parenchymatous
ground tissue of the fructification which, as in the Illinois species, seems to enclose
and "constitute the walls of the sporangia." It forms a network of uniform thick-
ness, 2-3 cells, composed of thin collapsed parenchyma in which are numerous
large secretory canals with their dark, opaque contents.
The double radial rows of tubular sporangia are separated by very conspicuous
sclerotic bands, 4-6 cells thick, which are normally interrupted at the junction
with the alternating lysigenous tubes but may occasionally form almost continuous
radial septa from the center of the fructification out to the marginal ground
tissue. The individual sclerotic fibers are small, 50 /t in diameter and up to
500 1t in length. The bands bifurcate from 1 to 3 times, the first time about 14
the distance from the center, the second at about half the distance from the center,
A 4 


[VOL. 36
316 ANNALS OF THE MISSOURI BOTANICAL GARDEN
Text-fig. 4. Dolerotheca sclerotica: Diagram showing pattern of bifurcations of
sclerotic-fibrous framework. a, campanulum wall. Explanation in the text. X 4.
and the third time within 1 mm. or less of the marginal peripheral ground tissue
(text-fig. 4). Additional paired rows of sporangia are intercalated at the inner
bifurcations while the marginal division is generally too near the periphery to allow
space for more than the insertion of a single sporangium. The lysigenous tubes are
much less conspicuous than in the three Illinois species. In the latter the tubes are
enclosed by walls 3-6 cells thick, having circular to oval locules, while the equiva-
lent structures in D. sclerotica are represented merely by rectangular spaces between
the thin (1 cell) tangential walls of adjoining sporangia (figs. 48 and 50). As in
D. formosa Schopf, the vascular bundles of our specimen "are noteworthy for their
obscurity." They consist of 3-4 small annular tracheids apparently restricted to
the marginal area of the campanulum. The bundles lie in the secretory parenchy-
matous tissue which alternates radially with the sclerotic bands, there usually being
but one bundle in each radial strand 1 mm. within the hypodermal zone.
D. sclerotica appears to have had considerably less dehiscence tissue than the
Illinois species, although the distinction is possibly doubtful since our specimen was
poorly preserved at the distal end. However, as shown in fig. 48, the groundwork
of the fructification consists solely of the fibrous sclerenchyma bands with
a parenchymatous network of secretory cells, and it is only at the extreme periphery
that fragments of tissue of possible dehiscent nature are found. The sporangia
average 500 X 700 p. in diameter, only the centermost being vertical. The outer
sporangia originate on the ascending inner slope of the campanulum and tend to


19491
BAXTER-FOSSIL PTERIDOSPERMS 3)1/
follow the general shape, curving outward and upward (fig. 45). The spores are
unusually large averaging 470 X 200 t, in the longer dimension exceeding that of
all of the Illinois species. They are marked by a monolete suture similar to that
described for D. formosa.
The major distinctions between D. sclerotica and the three Illinois species-
D. villosa, D. Reedana and D. formosa-are as follows:
1. Few very small capitate epidermal hairs as compared to the relatively dense
pubescence of the other three species.
2. A homogeneous sclerotic hypodermal zone.
3. Lysigenous tubes which are merely gaps between thin-walled sporangia.
4. A dominating radiating framework of bifurcating fibrous sclerenchyma
bands.
5. A greater amount of secretory cells in the parenchymatous ground tissue.
6. Larger prepollen or spores.
The differences may be said to be almost of generic importance and scope and
lend further weight to the viewpoint voiced earlier that the Medullosae are prob-
ably a more heterogeneous group than can much longer be contained in a single
genus.
Diagnosis:
A flattened campanulum up to 25 mm. in diameter. Epidermis of dark secre-
tory cells, practically glabrous, with only a few capitate hairs. A conspicuous
hypodermal zone of isodiametric sclerenchyma cells. Groundwork composed of
radiating, bifurcating bands of fibrous-sclerenchyma enclosing a parenchymatous
secretory tissue which composes the sporangial walls. Lysigenous tubes consisting
solely of gaps between thin tangential sporangial walls.
Horizon: Des Moines Series, Pennsylvanian.
Type: Fig. 45. Slide 1628, in the paleobotanical collections of the Henry Shaw
School of Botany of Washington University.
Dolerotheca Schopfii, sp. nov.:
This species, like D. sclerotica, is based on a single specimen also from the What
Cheer coal mine near the town of What Cheer, Iowa. The fructification had evi-
dently been broken into fragments prior to fossilization since, although cellular
preservation is excellent, only an estimated one fourth or less of the campanulum
was present in the coal ball. However, from the individual sporangia (up to
.6 X 1.3 mm. in diameter and their incomplete length of 15 mm.) it is possible to
assume that the complete structure was comparable in size to D. formosa and pos-
sibly more tubular due to its apparent greater depth (figs. 51 and 53). Thus, it
is considerably larger than D. sclerotica. Unlike the latter species also, its proximal
surface is covered with an extremely dense pubescence of glandular hairs up to 5-6
cells in length. The cells are flattened, 3-4 times as broad as long, the terminal
cell being slightly tapered. Ail the cells contain black opaque secretory masses
 t *m!r


[VOL. 36
ANNALS OF THE MISSOURI BOTANICAL GARDEN
(fig. 57). In the solid density of the hairs D. Schopfii is comparable to D. villosa
but the gross appearance is closer to D. formosa.
Immediately within the hirsute epidermis is a broad (up to 1.5 mm. thick)
hypodermal zone of large secretory canals (200 u in diameter) scattered profusely
throughout a homogeneous matrix of small fibrous sclerenchyma cells which average
50 p in diameter to 500 i in length. This zone is identical to and continuous with
the ground tissue making up the tangential and central radial walls of the paired
sporangia (figs. 46 and 47). The radiating framework of fibrous, sclerotic bands
is not quite as prominent as in D. sclerotica but is still much more extensive than
in any of Schopf's Illinois species. As in D. sclerotica, the radial bands are oc-
casionally continuous for a space of 2-3 sporangia, although the more usual con-
dition seems for the bands to have been interrupted at the point where they join
the sporangial tangential walls (fig. 51). The individual fibers are approximately
equal in size to those of D. sclerotica.
Probably the most distinctive character of the species is the apparent lack of
lysigenous tubes which in the other species alternate radially with the tubular
sporangia. While the fragmentary condition of the type specimen shows only a
marginal portion of the original campanulum to a depth of about 6 sporangia, it
can be clearly seen that the radially adjoining sporangia are separated only by a
common wall of the secretory and sclerotic ground tissue (figs. 46 and 51). It is,
of course, possible that this could represent an immature stage in which the cellular
disintegration forming the lysigenous tubes had not yet taken place. However, the
size of the fructification, which must represent considerable maturity, along with
the apparent complete dehiscence of the spores, makes it seem much more likely
that the lysigenous tubes were simply not developed in this species.
The vascular bundles are even more obscure than in D. sclerotica. They con-
sist of only 1-2 annular tracheids and occupy a similar marginal position in the
radial ground tissue just within the broad hypodermal zone.
As in D. sclerotica, there is no observable dehiscence tissue, which again may
possibly be due to lack of sections through the distal end. Dehiscence had cvi-
dently been complete, and no spores were found in any of the sporangia.
In comparison with D. sclerotica and the three Illinois species the following
characters of D. Schopfii are held to be of specific importance.
1. Absence of lysigenous tubes.
2. The broad secretory and sclerotic hypodermal zone continuous with and
identical to the groundwork making up the sporangial walls.
3. The more tubular shape of the campanulum.
While the nearly glabrous stony outer tissues of D. scclrotica contrast strongly
with the dense glandular hairs and thick secretory zone of D. Schopfii, the thick
radial sclerotic framework in both, along with inconspicuous lysigenous tubes in
D. sclerotica and complete lack of them in D. Schopfii, seems to show that the two
species are much more closely related to each other than to the Illinois species.
318


1949]
BAXTER-FOSSIL PTERIDOSPERMS ) IY
The species is named in honor of Dr. James M. Schopf in recognition of his
noteworthy work on the genus.
Diagnosis:
Campanulum an estimated 35 mm. in diameter and 15 mm. or more in depth.
Proximal epidermis with a dense pubescence of broad glandular hairs; a broad hypo-
dermal zone of large secretory canals in a homogeneous matrix of small fibrous
sclerenchyma which is continuous with and identical to the groundwork forming
the sporangial walls. Lysigenous tubes lacking, adjoining sporangia having a com-
mon tangential wall.
Horizon: Des Moines Series, Pennsylvanian.
Type: Fig. 51. Slide 1629 in the paleobotanical collections of the Henry Shaw
School of Botany of Washington University.
Discussion:-
While accurate geological correlation of the horizon of the Des Moines Series
producing these and other petrifactions described in this paper is still needed, the
evidence of the fossils themselves would tend to indicate a position in the lower part
of the series and possibly considerably older than the Carbondale of Illinois. This
viewpoint is based on the following facts: Over a period of three years of investi-
gating hundreds of coal balls from Illinois and Iowa (i.e., the Des Moines Series)
what appear to be the more primitive plants are ail from the latter horizon. Micro-
spermopteris aphyllum (described earlier in this paper), with its very primitive
habit and psilophytalian characters, is from the Des Moines Series; also Medullosa
primaeva and M. Thompsonii, both of which have been tentatively placed at the
bottom of the phylogenetic chart (text-fig. 2) as representing the most primitive
stages of the known species. Dolerotheca sclerotica and D. Schopfii, with their
large amount of sclerotic tissue, seem closest to D. Reedana which, in being from
the Carbondale of Illinois, is the oldest of Schopf's three species. In addition, D.
sclerotica and D. Schopfii, with their much more extreme sclerotic condition, ap-
parent lack of dehiscence tissue, simple lysigenous tubes or complete absence of
them, and larger prepollen size (in D. sclerotica), seem to indicate an evolutionary
stage considerably below that of D. Reedana.
Since the much younger Dolerotheca formosa shows only isolated groups of
sclerenchyma and D. villosa appears to lack them completely, the primitive
state would seem to have been the almost complete radial septation (of a single
telome?) by bands of fibrous sclerenchyma between which were borne the essentially
independent radial rows of paired sporangia. If any other proof were necessary to
show the radial rather than cyclic arrangement of the sporangia in Dolerotheca
(Schopf, 1948) it is amply supplied in D. sclerotica with its almost continuous
radiating network of fibrous-sclerotic bands. In addition, the more numerous and
regular bifurcations of the radial framework and the nearly symmetrical inter-
calation of additional paired rows of sporangia seem indicative of a centrifugal
direction of development.


[VOL. 36
320 ANNALS OF THE MISSOURI BOTANICAL GARDEN
Found in close association with D. Schopfii was the Myleoxylon fragment shown
in fig. 54. A longitudinal section through its outer margin, in fact, shows the base
of the fructification with its tissues apparently continuous with those of the
petiole (fig. 52). While the continuity of tissues is not so complete as to allow a
definite statement as to their connection, the association is extremely close and felt
to be worth illustration and mention. If this condition does represent a true at-
tachment it would seem to show that, unlike D. Reedana, D. Schopfii was sessile
and attached directly to fairly large divisions of the rachis.
SUMMARY
1. The known Carboniferous flora is outlined and it is suggested that it falls
into large tree-like, microphyllous groups and small shrubby or climbing mega-
phyllous groups with the pteridosperms being in the latter category. The char-
acters of the pteridosperm stem genera are given, and it is emphasized that they
constitute a clearly defined group irrespective of the lack of knowledge as to
whether they bore seeds or sporangia.
2. A new unique plant based on a stem with pteridosperm characters is de-
scribed and discussed. Named Microspermopfcris aphyllum because of its very
small size and leafless condition it offers evidence for the origin of the secd-ferns
from the Psilophytales, as well as for megaphyllous leaf development. It combines
characters of both Lyginopteris and Heterangium and appears to have possibly been
ancestral to both.
3. Three new species of Medullosa are described, and a new phylogenetic
viewpoint presented. The evidence for a climbing or creeping habit for the group
is given, new evidence being offered for a bilateral, dorsi-ventral habit.
4. Some excellent new material of Medullosa Noci is described with particular
reference to new data on the conspicuous phloem rays, adventitious aerenchymatous
roots, and periderm or "cambial" rings which appear similar to the star rings of
the Permian species. "Star rings" are discussed in general, and it is shown that
the fourth small stele of Medullosa centrofilis had nothing in common with the
"star rings" of the Permian plants. "Aggregate leaf traces" in Medullosa Thol p-
sonii are described and compared to Permian "star rings."
5. The microsporangiate fructifications of Medullosa are discussed and two
new species of Dolerotheca are described. Evidence is offered that they constitute
the most primitive of the known species and show additional proof of a radial
rather than cyclic arrangement of the tubular sporangia. A very close association
with possible attachment is illustrated for a Dolerotheca and Myleoxylon. It is also
suggested that the plant remains from the Iowa coal balls may be of some aid in a
more accurate determination of the horizon of the Des Moines Series.
ACKNOWLEDGMENT
The author wishes to recognize the constructive guidance of Dr. Henry N.
Andrews under whose direction the present work was conceived and carried out.


19491
BAXTER-FOSSIL PTERIDOSPERMS 321
Thanks are also due Mr. Frederick O. Thompson of Des Moines, Iowa, for his ex-
tensive coal-ball collections which provided much of the investigated material, as
well as to Dr. J. M. Schopf and R. M. Kosanke, for their cooperation on the
Dolerotheca section.
BIBLIOGRAPHY
Andrews, Henry N. (1940). On the stelar anatomy of the pteridosperms, with particular ref-
erence to the secondary wood. Ann. Mo. Bot. Gard. 27:51-118.
-- -, (1945). Contributions to our knowledge of American Carboniferous floras. VII. Some
pteridosperm stems from Iowa. Ibid. 32:323-360.
- - , (1948). Some evolutionary trends in the pteridosperms. Bot. Gaz. 110:13-31.
---, and Kernen, J. A. (1946). Contributions to our knowledge of American Carboniferous
floras. VIII. Another Medullosa from Iowa. Ann. Mo. Bot. Gard. 33:141-146.
Arnold, C. A. (1940). Structure and relationship of some Middle Devonian plants from western
New York. Am. Jour. Bot. 27:57-63.
(1947). An Introduction to Paleobotany. New York.
_ , (1948). Classification of gymnosperms from the viewpoint of paleobotany. Bot. Gaz.
110:1-12.
Benson, M. (1933). On the roots and habit of IHeterangium Griecii. Ann. Bot. 47:313-315.
Bower, F. O. (1930). Size and Form in Plants. London.
De Fraine, E. (1912). On the structure and affinities of Sutcliffia, in the light of a newly discovered
specimen. Ann. Bot. 26:1031-1066.
, (1914). On Medullosa centrofilis, a species of Medullosa from the Lower Coal Measures.
Ibid. 28:251-264.
Halle, T. G. (1916). Lower Devonian plants from Ruragen in Norway. Kgl. Svenska Veten-
skapsakad. Handi. 57:1-43, pl. 1-4.
Hirmer, Max (1933). Zur Kenntnis der Structurbietenden Pflanzenreste des jungeren Palaeozoikums.
Palaeontographica 77, Abt. B.
HIoeg, O. A. (1937). The Devonian floras and their bearing upon the origin of vascular plants.
Bot. Rev. 3:563-592.
Lignier, O. (1908). Essai sur l'evolution morphologique de r�gne v�g�tal. Soc. Linn. Normandie,
Bull. VI, 3:35-62.
Sahni, B. (1920). On the structure and affinities of Acmopyle Pancheri Pilger. Roy. Soc. (London),
Phil. Trans. B. 210:253-310.
Schopf, J. M. (1939). Medullosa distelica, a new species of the Anglica group of Medullosa. Am.
Jour. Bot. 26:196-207.
- , (1948). Pteridosperm male fructifications: American species of Dolerotheca, with notes
regarding certain allied forms. Jour. Paleont. 226:681-724, pis. 104-115.
Scott, D. Il. (1899). On the structure and affinities of fossil plants from the Palaeozoic rocks. 3.
On Mnullosa anglica, a new representative of the Cycadofilicales. Roy. Soc. (London), Phil.
Trans. B. 191:81-126.
, (1914). On Medullosa pusilla. Roy. Soc. Lond. Proc. B. 87:221-228.
, (1917). The Heterangiums of the British Coal Measures. Jour. Linn. Soc. (London),
Bot. 44:59-104, pl. 1-4.
-----, (1923). Studies in Fossil Botany. London.
Seward, A. C. (1917). Fossil Plants. Vol. 3. Cambridge Univ.
Solereder, IH. (1908). Systematic anatomy of the Dicotyledons. Vol. 2. Oxford.
Steidtmann, W. E. (1937). A preliminary report on the anatomy and affinities of Medullosa Non
sp. nov., from the Pennsylvanian of Illinois. Am. Jour. Bot. 24:124-125.
_- - , (1944). The anatomy and affinities of Meduillosa Noci Steidtmann, and associated foliage,
roots, and seeds. Univ. Mich., Contrib. Mus. Paleont. 6:131-166.
Thiessen, R. (1920a). Composition and compilation of bituminous coals. Jour. Geol. 28:pl. II,
fig. 42.
, (1920b). Structure in Paleozoic bituminous coals. U. S. Bur. Mines, Bull. 117:pl. 151,
fig. A-B, pl. 152, 153.
Weber, O., und Sterzel, J. T. (1896). Betrage zur Kenntnis der Medulloseae. Naturwiss. Ges.
Chemnitz, Ber. 13:44-143.
Westermaier, M., und Ambronn, H. (1881). Beziehungen zwischen Lebensweise und Structur der
Schling- und Kletterpflanzen. Flora 64:417-430.
Wilson, Carl L. (1942). The Telome Theory and the origin of the stamen. Am. Jour. Bot.
29:759-764.
Worsdell, W. C. (1906). The structure and origin of the Cycadaceae. Ann. Bot. 20:129-159.


322
[VOL. 36, 1949]
ANNALS OF THE MISSOURI BOTANICAL GARDEN
EXPLANATION OF PLATE
PLATE 2
Microspermopteris aphyllum
Fig. 1. Cross-section of a mature stem showing departure of a collateral branch
bundle. From slide 1602, X 20.
Fig. 2. Same specimen a few peels above the preceding figure. Branch bundle is
becoming concentric. From slide 1603, X 20.
Fig. 3. Cross-section of a small stem (branch?): a, beginning of branch vascular
bundle departure; b, sclerotic plate. (See fig. 55 which shows a later stage of branch
bundle departure on same stem). From slide 1604, X 20.
Fig. 4. Enlargement of the stele of a heptarch adventitious root. (Sec fig. 56 for
appearance of complete cross-section). From slide 1605, X 50.


ANN. Mo. Boi. G(AD., Vo.. 36, 1949
I 71
3
BAXTI R-FOSSI 1 PiT RIDOSPI RIMS
Pl fii 2


324
[VOL. 3(;, 119]9
ANNALS OF THE MISSOURI BOTANICAL GARDEN
�IXPI AN ATION 01 Pl ATI
P1 ATI 3
A/i'rfj >r n  /c7.r�i a<pi) ) l/u
:i . 5. Cross section of sami stem as in tigs. I and 2, showing the horizontal passage
aof thc branch a.scular bundle; a, forked cmergencc. F rom slide 1606, ' 18.
it. . (ross-section taken a few peels abhove the preceding tigure showing departure
of an adventtiious root; root r halis curved downwards and out of thc cortex. I'rom slide
1607, 4 18.
F ig. 7. C(ross-section of a more mature stem showing unequal xylem development;
ia, sclerotic plate just within thc epidermis. F:rom slide 1608, X 15.


ANN. Mo. M Bor. (GAR., Vol. 36, 1949
BAXTIlR- FOSSII PTIRI)DOSPI:RMS
PiLAT 3
~~


326
[VOL. 3(6, 0m11
ANNALS OF THE MISSOURI BOTANICAL. GARDEN
EXPlA NAIION 01 Pi AIl
Pl.A'Tl 4
Muirs, pero IO lrih a 1 hyli un
Sig. S. Radial section of stem: '-, sccondarv xvlem; /(, inner cortex: OC, outer
cortex; SP, sclerotic plate; cm, emergencc. I rom slide 1609, X 50.
Fig. 9. Tangential view of secondary wood showing small uniseriate ravs and pitting
in tangential walls. From slide 1610, X 1 35.
Flig. 10. Radial section of stem showing sclerotic plates in outer cortex just within
epidermis. Irom slide 1611, X 53.
Fig. 11. Tangential section through outer cortical zone showving anastamosing hori-
zontal plates. From slide 1612, X 25.
IFig. 12. Reticulate bordered pitting in wsall of a metaxyiem tracheid. From slide
1613, X 450.


AN\. Mo. BoI . GS )., Vol.. 36, 1949 lI xII 4
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328
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IVni. 3f, 19491
ANNALS OF THE MISSOURI BOTANICAL GARDEN
EXPLANATION o0 Pi ATU
IPIATI 5


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330
ANNALS OF THE MISSOURI BOTANICAL GARDEN
EX PI.A NATION OF Pi ATI
PI.AT 1 6,
I 'dull<>ia f'rimii ati a
F ig. 13. Transvcrse-longitudinal view i)f type specimen showing branching and fusing
of the stelcs: a, small stele in a horizontal course throutgh the stem; Si, 52, S,, and S./
show portions of stcles indicatcd in ncxt tinureC. lrom slide 1614, : 4.5.
Fig. 14. Transverse section of top surface of type sp�cimen: SI, S2, Sj, Sj, Si, SO,
S7, and SN indicate the eight steles. From slidc 1615, X> 6.2.
Fig. 15. Transverse section of bottomi surface of type specimen. Stules bave partially
fused. IFrom slide 1616, X 6.2.


PIATE. 6
ANN. Mo. BOT. GARD., Voi. 36, 1949
13
f ~ -
14
15
BAXTIER-FOSSIL PTERIDOSPERMS
ai
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Imm


1 Vor.. 3(, I1941
332 ANNALS 01 THE MISSOURI BOTANICAL GARDEN
EXPl.ANA IION 01 Pi A T
Pl'IATI 7
MlJulhllla .iln<gctal
Itig. 16. Transverse view of complete type specimen: a and b, latcral leaf bases; c,
dorsal leaf base. From slide 1617, X 2.5
Fig. 17. E:nlargement of central portion of stem shown in fis. 16 to show the details of
the three steles. Note narrow line of primary wood in lower left-hand stelc. From slide
1617, X 6.5.
Fig. 18. Compound resin canals which run horizontally throuigh the stem. From slide
1618, X 6.5.
Mcdullswa primacic a
Iisg. 19. lEnlargement of steles Si and S2 from fig. 14. Note almost solid protosteles.
l'rom slide 1615, X 16.


ANN. . Mo. BOT. (;.\R.. YoI. 16, 1949
19
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[ \V(.. 3l, 1941'1
334 ANNALS OF THE MISSOURI BOTANICAI GARDEN
EXPI ANATION 01 Pi AxI
PlATll s
M c/dullosw e'alncer /riica
Fig. 20. Transverse section of stelar assembly of type specimciin with cnclosing "peri
derm": a, third small stele; b, phlilocm zone; XI, primary xylem. F:rom slide 1619, y 10.
Fig. 21. Transversc-tangential section showing verv broad rays in "philom" 'irci.
Above point indicated by (a) is transverse, below tangential. From slidc 1620, X 40.
Fig. 22. Tangential-transvcrse section through secondary xylcm showing narrow (1-2
cells wide) rays; a indicates line between transverse and tangential views. From slide 1621,
X 40.
Fig. 23. Portion of a transverse "sieve plate" from one of the large "sieve tubes" of
the phloem zone. I rom slide 1620), 650.


ANN. . Mo. IBo. CGhA., o . V. 3, 1949
BAXTI R--FOSSII P'TI RII)OSPIERMS
PLAr_ 8


336
i \ l.. . 1 9- i
ANNALS O0F THE MISSOURI BOTANICAL GARDEN
EXPIIANAVII ON 1. PI.Al'.
l lA'II ii
\lcJlloa Noei
l i . 24. A single "ciamlbial ring" showxini development of secon dary wood. I)ark cen-
trail area is composed of primary trach.ids and pa rcnch im.. I rom slidc I 622, X 9.
Fii. 25. A single wcll-preserved cortical, pcntarch root. Note e:lni )sin peridcrm and
acerenchymatous cortex. I:rom slide 1623, P_ 14.
1 p. 26. Marginal portion of a stele showing fringe -,f expandcd phloem ravs. IFrom
slide 1624, "<' 12.
A'l i e, lloa pri rtUai a
Fig. 27. Longitudinal section throughl cortex showing spiral thickeninn in a leaf trace.
From slide 1625, Y 95.


ANN. Mo. Bor. GARD., l. 36, 1949
26
24
BAXTIR-FOSSI L PTIR I1)OSIPERMS
P1>A 1i 9
) /
25


I OL. 3 , 19 1]
338 ANNALS OF THE MISSOURI BOTANICAL GARDEN
EXPIANATION 01 PI.ATI
PIA T 10
"Star Rings"
Fig. 28. A "cambial" or "periderm" ring from M. Nori in which radial rows of
secondary xylem have formed. From slide 1622, X 5.5.
Fig. 29. A "star ring" from M. stflalata v. Cotta a. typica, at the same magnification as
the above (after Weber and Sterzel), X 5.5.
Fig. 30. An "aggregate leaf trace" from M. Thompsoonii (sec fig. 59b). From slide
1626, X 13.7.
Fig. 31. A single small stele of M. primait a. From slide 1 61 5, X 20.7.
Fig. 32. "Star Ring" of M. rcn/rofilis (after De �raine), X 20.7.


ANN. Mo. BOT. GARD., VOL. 36, 1949
w
BAXTII:R-FOSSIL PITERIDOSPERMS
PLATE 10


[Voi. 3(, 194)1
ANNALS OF TIHE MISSOURI BOTANICAL GARDEN
340
XPA NAI ION 01 Pi A Il
PIATI: I I
Di)agrams of the stelar assemblies with enclosing periderm (where present) of aill of the
Carboniferous species of lMcullosa with the exception of MA. Leuckarli. The magnification
is 2.8, and ail of the diar.ams other than figs. 34, 36, 42, and 43 are taken from Andrews
(1945, 1946). The primary area of the stele is shown as solid black, the secondary wood as
radiating lines, and the periderm as enclosing double or dotted lines depending on whether
it was actually observcd or was partially assumed.
Fig. 33. M. r/itlrufilis De Fraine; Fig. 34. M. /,rimani a Baxter; 1 ig5 .5. M. Thomup-
softii Andrews; FIig. 36. M. ciduoci�n'triwa Baxter; Fig. 37. M. anglica Scott; Fig. 38. AM.
his/elica Schopf; FIig. 39. M. pusilla Scott; Fig. 40. AI. anglica var. T/hI e lni Schopf.
(Continued on pl. 12)


ANN. Mo. Bor. GARD., VoI.. 36, 1949
39
40
BAXTIER-FOSSIL PTERIDOSPI1RMS
PLATE 11


342
I [\L. 36, 1949)1
ANNALS OF THE MISSOURI BOTANICAL GARDEN
EXPLANATION OF PLATE
PLATE 12
Fig. 41. M. anglica var. ioensis Andrews; Fig. 42. M. elongatla Baxter; Fig. 43. M.
Noci Stcidtmann, showing only about half of two of the stem's three steles. (M. Noei is so
much larger than any of the other species rcpresented here that one complete stele at X 2.8
magnification would more than fill an entire plate.) The white ring within the black
primary area (in the upper of the two stele halves) represents a "cambial ring" as shown
in figs. 24 and 28.


ANN. Mo. Bor. GARD., Voi. 36, 1949
41
\
I
1
I
I
BAXTER-FOSSIL PTERII)OSPERMS
PLATEr 12
I


344
[Vol.. 3(,, l94'I
ANNALS OF THE MISSOURI BOTANICAL GARDEN
EXiPLANATION 01 PLATl
PLATE 13
Dolerotheca formosa
Fig. 44. Transverse-longitudinal view of a portion of a complete campanulum. Below
the line a-hb is the longitudinal eut; above, the transverse. In comparison with the following
figure note the large lysigenous tubes and absence of a strong sclerotic framework. From
slide 1627, X 9.


PAl A 13
AsN. Mo. BoT. GARD., Voi. 36, 1949


[ Vo.. 36, 19401
346 ANNALS OF THE MISSOURI BO1ANICAL GARDEN
EXPI ANATION 0F Pi.AT':;
PLiATI 14
Dole rot heeca sci'lrotica
Fig. 45. Transversc-longitudinal view of entirc fructification. Below the line al- is the
longitudinal eut showing thc curving of the marginal sporangia; above is the transverse eut
showing the bifurcation of the thick sclerotic bands, between which can be sccn the par-
enchymatous-secrctory tissue forming the sporangiaI walls. The upper right-hand margin
shows the sclerotic hypodermal zone. le'or more detailed view sec figs. 48 and 49 from
slide 1628, x 9.


ANN. Mo. BOT. GARu)., Vo.. 36, 1949 PILATI 14
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I
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348
[r\oL 3. 13i.
ANNALS OF THE MISSOURI BOTANICAL GARDEN
EXPelANAIION 01= PLATI
PI.ATI 15
Fig. 46. Doleroth'ca Scho[pfii. Transverse view of a double row of tubular sporangia
showing four empty sporangia separated by the slime canal and sclerotic ground tissue and
enclosed on the left and right by the thick sclerotic bands. Note absence of lysigenous
tube between sporangia; sp, sporangium. FIrom slide 1629, X 22.
Fig. 47. Dolerot e'ca Schoplfi. Transverse vicw of campanulum wall showing pubes-
cent epidermis and secrctory-sclerotic hypodermal zone; a, glandular hairs. Sec fig. 57 for
detail of hairs. From slide 1629, X 40.
Fig. 48. Doleroitwera sclerotic'a. Transverse view of a double row of sporangia sep-
arated from portions of two other rows by the thick sclerotic bands. Note thin-walled
lysigenous tubes alternating radially with the sporangia and bifurcation of the sclerotic
bands; sp, sporangia; 1, lysigenous tubes. From slidc 1628, X 32.
F ig. 49. Dole'rotbel a scZcrotic'a. Transverse view of campanulum wall showing epi-
dermis and sclerotic hypodermal zone; sp, sporangia. From slide 1628, X 40.
F:ig. 50. Dolerothe'a forimosa Schopf. Transverse view of a double row of sporangia
with the alternating smaller lysigenous tubes. a and b indicate the much less conspicuous
sclerotic bands than in figs. 46 and 48; .s, sporangia; 1, lysigenous tubes. From slide 1627,
X 32.


PLAiT 15
ANN. Mo. Bo. GARI)., VoL. 36, 1949
47
46
49
50
IAXTI R--1OSSIL PT1:R II)OSPI R MS


350
[VOL. 36. 14'1 |
ANNALS OF THE MISSOURI BOTANICAL GARDEN
EX PLANATION F0 Pi.A T1
PLATE 16
Fig. 51. Dolero/t/hca Schopfii. Transverse view of marginal portion of campanulum:
a, broad slime canal and sclerotic zone forming the wall of the fructification partiy broken
away from inner tissue. Sec figs. 46 and 47 for detail. From slide 1629, X 8.
Fig. 52. Doleh'rot/ra Schohfii: a, oblique-longitudinal view showing possible attach-
ment to Mylcoxylon sp. at point indicated by c; b, longitudinal view of hypodermal zone
of Myl oxylon sp. shown in fig. 54. From slide 1630, X 8.
Fig. 53. Dolero/hwca Sciholfi�i. Longitudinal view of marginal portion of campanulum
showing the ascending origin of the outermost sporangia. From slide 1629, X 8.
Fig. 54. Myheox lon sp. Transverse view of petiole shown in fig. 52b. From slide
1630, X 9.


ANN. Mo. BOT. GARD., Vo.. 36, 1949
51
4,
If
54
53
BAXTER-FOSSIL PTERIDOSPI'>RMS
PLA'T} 16
-ti
,i:


1 Vol. 3 ,, l 41)
352 ANNALS OF THE MISSOURI BOTANICAL GARDEN
EXPLANATION 01 Pi A1 1
PIATE 17
Fig. 55. \Alicrospermoj/ t 'ri. r aiphltum. Cross-section of small stem or brandi showing
departure of branch bundle. This represents a stage shortly above that shown in tig. 3.
From slide 1632, X 26.
Fig. 56. Micros<prmoDrteris aipd'llinni. (ross-section of an adventitious root. Front
slide 1633, X 34.
J ig. 57. 1)oler.thl'ca Schptlii. I)rawing of epidermal hairs. IFrom slide 1629, X 350.
i ig. 58. 1)olerothe a sci 'rtica. I)rawing of one of the rare glandular epidermal
hairs. From slide 1631, X 550.
Fig. 59. M'ed<llosa 7'/homnpsonii. I)iagramn of central portion of the stem: a, stelar
assembly; b, line of "aggregate leaf traces" at point just above the departure of a petiole
as indicated by absence of hypodermal tiber strands shown at c. Sec fig. 30 for detail of
a single "aggregate trace." From slide 1626, X 4.


ANN. Mo. BOT. GAIRI., Votl. 36, 1949
57
58
BAXTER-FOSSIL PTERIDOSP-ERMS
PLATEI 17