THE ANNALS 
AND 
MAGAZINE OF NATURAL HISTORY. 
[TfflRD SERIES.] 
" perlitora spargite museum, 
Naiades, et circilm vitreos considite fontes : 
Pollice virgineo teneros hic carpite fiores : 
Floribus et pictum, divse, replete canistrum. 
At vos, o Nymphje Craterides, ite sub undas ; 
Ite, recurvato variata corallia trunco 
Vellite muscosis e rupibus, et mihi conchas 
Ferte, Des pelagi, et pingui conchylia succo." 
N, Parthenii Giannettasii Eel. 1. 
No. 67. JULY 1863. 
I. — On some Phenomena of the Development of the Organic Cell. 
By Prof. H. Karsten*. 
[Plate L] 
1 HE physics of the development and of the life of the cell, 
as the basis of all anatomy and physiology, constitute the first 
problem to be solved in both those sciences. Since Schwann 
declared that both animal and vegetable tissues consist of cells 
originally of a like nature, the similarity also in function of such 
cells both in animals and plants has been rendered more and 
more evident, 
A clear perception of the whole of the physico-chemical phe- 
nomena which by their union constitute life will only be attained 
by an accurate knowledge of the origin and growth of the cell. 
The formative elements of the cells which unite to constitute 
organic tissues have been largely investigated since the time 
when Robert Brown indicated the presence of a nucleus in nu- 
merous cells, and since I demonstrated that the cell-wall, pre- 
viously regarded as a single sac, consists in reality of several 
endogenous superimposed laminse (Karsten, De Cella vitali, 
]843). 
* Translated by Dr. Ai'lidge from a separate impression from Poggen- 
dorff's ' Annalen' (vol. cxviii., Berlin, 1863), for the communication of which 
we are indebted to the author. 
Ann. ^ Mag. N, Hist. Ser. 3. Vol. xii. 1 
2 Prof. H. Karsten on some Phenomena of 
The primary object at present is to determine the physical 
and chemical changes of the histological elements of cells during 
their development and multiplication, and, by the elucidation of 
these processes, to establish the laws which govern the origin 
and growth of an organ or of an organism, and which collec- 
tively make up the phenomena of life. 
The most recent treatise on human histology, that by Kolliker 
(1862), refers to the purpose of the diflferent histological elements 
of the cell, in respect both to its existence and its functions, 
thus : — 1 . The external wall of the cell serves only as a defence 
to its fluid contents (p. 39), except so far as it takes part in those 
intrinsic vital processes which are shown to occur by changes in 
its chemical constitution (p. 36) ; 2. the fluid cytoblastema pre- 
eminently constitutes the living portion of the cell (p. 39) ; and, 
3. the cell-nucleus plays the most important part in cell-formation 
(p. 26). 
This last proposition is advanced on the understanding that 
" the doctrine of free-cell formation in a cytoblastema has been 
set aside'' (p. 28) — that cell-construction always coincides with 
cell-multiplication, being a result of the fission of a parent 
cell by means of the formation of folds in and the constriction 
or segmentation of its internal lamina (the primordial layer), 
although Kolliker fails not to remark that this process has, it 
is true, not yet been satisfactorily made out. 
These fundamental doctrines of the histology of the animal 
body, which harmonize with the prevailing, but groundless, 
opinions upon the formation and function of the vegetable cell, 
have, however, not been confirmed in the vegetable organism 
with the clearness necessary for conviction. The history of 
development has rather proved that, in those cases (Karsten, 
op. cit. and Histologische Untersuchungen *, 1862) which have 
been cited as furnishing certain evidence of the multiplication of 
cells by segmentation, daughter cells, which originate freely in 
the fluid contents of the parent cell, cause the increase, and by 
their enlargement the division of the cell-interior by means of 
septa is brought about. 
Moreover the wall of the cell is not simple, but composed of 
several cells placed one within the other, which are frequently 
regenerated from within outwards by the unfolding of the nuclear 
cell, and each of which cells passes through a course of develop- 
ment peculiar to itself. 
The involution of the coats of the cell, in the few tissues 
where it has as yet been actually observed, does not give rise to 
* A translation of these valuable investigations will appear in a future 
Number of the ' Annals.' 
the Development of the Organic Cell. 3 
new cells, but is only a phenomenon passively accompanying 
cell-multiplication. 
The so-called nucleus is a nuclear cell possessing the faculty 
of development, though frequently suppressed in the course of 
development, and near to or within which two or more new cells 
(cell-nuclei) may arise in order to carry on the multiplication of 
the individual cell in question. Mirbel taught, and Mohl co- 
incided with his views, that the fission of the cell proceeded by 
the growth of centripetal septa, or of involutions of its wall, 
breaking up its contents into sections, the external surface of 
which became subsequently hardened into a firm lamina or spe- 
cial cell- wall ; and side by side with, but partially opposed to, 
this theory of cell-formation based on imperfect observations 
Schleiden afterwards enunciated his peculiar views on the 
function of the '^resting" nuclear cell — the cell-nucleus first 
observed by Robert Brown, which, in cells developing slowly, 
may be frequently met with. 
These opinions of Schleiden regarding the signification of the 
nuclear cell became a great impediment to advancing the know- 
ledge of cell-development. His followers entered so fully into 
the notion that the nuclear sac is the constant formative centre 
of the cell, exercising a catalytic efi"ect upon its fluid contents, 
whereby it brings about the precipitation from the surrounding 
fluid of a pellicular deposit around itself, that even those who 
regard the whole organism as built up by repeated multiplication 
of the first ovum-cell, resulting, as Mirbel supposed, from centri- 
petal involutions of the integument, consider this cell-nucleus 
as the starting-point in this mode of cell-multiplication. 
This involution is assumed to proceed, in these nuclear cells, 
in the same way as in the parent cell-membrane itself, by con- 
striction followed by division — each of the segments of the cell- 
nucleus deriving, by means of a folding and constriction of the 
inner lamina of its mother cell, a capacious envelope constituting 
the wall of a new cell. 
This process of nmltiplication of the nuclear cell (cell-nucleus), 
however, no more takes place than that of the mother cell by 
constriction. 
The so-called constrictions or segmentations of the cell-nucleus 
belong, in fact, to the same category as the so-termed germi- 
nating cells. These forms are produced by the excessive develop- 
ment of daughter cells in a feebly vegetating parent cell which 
is in course of destruction ; whilst the partial septa or folds in- 
terposed between the endogenous cells are not so much centri- 
petal growths as the result of a passive condition of the cell-wall 
at those parts. (The simultaneous growth of these septa with 
the endogenous cells is not indeed a matter of direct observa- 
1* 
4 Prof. H. Karsten on some Phenomena of 
tion ; on the other hand, their subsequent absorption has been 
observed in various instances.) 
That a cell-nucleus is, as a rule, present in actively growing 
cells, and that in withered cells or in those in a resting-state it 
disappears, corroborates the statement derived from direct ob- 
servation, that this nuclear cell possesses the property of deve- 
lopment in itself. 
Indeed the constant absence of nuclear cells in the normally 
detached cells of the epidermis of animals, and of the epithelium, 
in the cells of the tissue in the tail of the tadpole, in the woody 
cells of plants, &c., intimates the incapacity of such cells for 
further regeneration and individual development. 
As only the resting-form of the nuclear cell in tissue- cells has 
hitherto been recognized as the cell-nucleus, in many cases the 
nucleus has been denied to exist where actually present and, in- 
deed, in process of evolution, as, for instance, in tissues in con- 
tinuous course of regeneration, e. g. in muscular tissue, the endo- 
genous cells of which have at one time been considered nuclei, 
at another cells. 
And it follows that, in cells which do not undergo regeneration 
as lasting tissue-cells, nor self-multiplication, the nucleus is 
always absent. Such cells are met with in those vesicles that 
are produced in connexion with secretions, and are to be found 
usually in large numbers in the fluid contents of genuine cell- 
tissue. 
These generations of vesicles enclosed within a tissue-cell, and 
often engaged in constant formation and transformation, are 
the active instruments in the elaboration of organic material, 
transforming the inorganic matters dissolved in the cell-juices 
into combinations of a progressively higher grade. By means 
of the assimilative properties possessed by these simple cells, 
those substances are produced which either subserve the nutri- 
tion of the still assimilating membrane of the parent cell, or, 
where the cycle of its development is closed, are employed by 
the nucleus in the regeneration of the life-energy of the cell. 
Moreover, when the individual development of the cell has 
ended, and, together with the nuclear cell suppressed in its 
revolution and destined to its regeneration, two or more new 
daughter cells are formed and developed at the expense of the 
parent cell, these secretory materials are employed for this pur- 
pose ; and even after the formation of all such secondary ge- 
nerations is brought to a close, they are transferred by exosmose 
to other and remote parts of the organism to serve kindred 
purposes. 
Some of these secretion-cells have walls so much thickened 
{e. g. starch), or such opake and solid contents (e. g. chlorophyll). 
the Development of the Organic Cell. 5 
that, for a long time, they have been looked upon, as some even 
now are, as solid unorganized particles ; whilst others have such 
thin walls that they have either been overlooked, or else regarded 
as cavities in the less transparent and denser cell-contents. 
Such gaps in our knowledge of the structure of the cell 
render the right apprehension of its functions impossible, as is 
shown, for example, among other problems, by that of the 
phenomenon of the circulation of the sap, which has been so 
much canvassed, and regarding which a distinguished physiolo- 
gist has recently expressed himself in a manner which can only 
be explained by a misapprehension of the anatomical nature of 
the cell. 
In my 'Histological Researches' (p. 61) I have detailed my 
views I'especting the general cause of the circulation of the juices 
within cells ; and I will now describe the structure of the hairs 
of Urtica, which explains the apparently wonderful circulation 
within their large cell-cavities. In PI. I. figs. 1 & 3, is repre- 
sented a large hair of Urtica urens, with its cui-ved and rounded 
extremity. The large hair-cell, under a low magnifying power, 
appears filled with a colourless though somewhat turbid liquid, 
and has an inferior rounded extremity surrounded by an epi- 
dermic layer of cells. On the wall (as in fig. 1) or in the me- 
dian line (in fig. 2) of the portion of the hair-cell which pro- 
jects freely from the cup-like base is seen a large nuclear cell 
filled with a whitish mucilaginous substance and a nuclear ve- 
sicle. At times, particularly in fully grown stages, this organ 
is concealed by the cellular envelope at their base. 
By rather stronger magnifying powers, it becomes evident 
that this nucleus is the central point of currents of a turbid 
finely granidar fluid, which spreads itself more or less com- 
pletely over the inner surface of the thick wall of the hair. By 
a little attention, it is further seen that the streams which pass 
across the interior of the cell are not all thread-like, as appears 
at first sight, or at least are not constantly so, but in part 
coalesce into a thin layer of fluid, which here and there, espe- 
cially in the lower portion of the hair, gets collected in the form 
of a thicker column, usually more rapid in its course. The 
fibre-like stream is also as little constant in character as the 
wider but thinner current : at times it flows rapidly, at others 
slowly; at one time the tenacious-looking granular fluid collects 
in one place, at another it breaks away from the locality in 
which it has been confined, to extend to other parts, and thereby 
sufi"ers some change in its direction. A rapid current is esta- 
blished especially after the hair has been placed in water under 
the microscope for a short time, as from two to three minutes, 
— a circumstance, no doubt, due to the diff"usion of the water. 
6 Prof. H. Karsten on some Phenomena of 
The circulation then proceeds for several hours, becoming weaker 
and weaker, until it at length entirely ceases, the fibres of the 
cloudy fluid growing more obscure, from an apparent coalescence 
within the interior of the cell. 
The central nuclear cell, moreover, usually sank, daring these 
phenomena, lower down in the cell ; and the same organ, when 
attached to the wall, often showed also a slight change of place. 
The largest portion of the upper extremity of the cell is 
usually divided, by only one obliquely directed stratum of circu- 
lating fluid, into two long sections; but its lower portion is 
broken up into several rounded clear spaces by shorter layers. 
In the interspaces formed by the contiguous borders of three 
such clear spaces, as also in the canals running along the wall 
of the cell, bounded by the adjoining sides of other two, circu- 
late more rapidly the usually thicker, filiform and more visible 
threads. 
Hence it is evident that the internal cavity of the thick- walled 
large hair-cell is subdivided into several hollow spaces, filled 
with a transparent homogeneous fluid, and that these spaces are 
capable of undergoing some change of form very gradually, and 
are separated from one another and from the external wall, more 
or less completely, by means of a system of mucous currents. 
There also exist within the interior of the hair-cell, betwixt 
the spaces filled with homogeneous watery fluid, other spots 
unoccupied by the turbid matter in circulation; or such are 
seen to originate under the eye of the observer by a disintegra- 
tion of the circulating substance. At such spots the larger 
clear spaces are therefore separated by very thin dissepiments. 
All these conditions bear testimony to the fact that the hair-cells 
of Urtica urens, and, in fact, many parenchymatose plant-cells, 
are occupied, at a certain stage of their development, by a tissue 
composed partly of non-nuclear cells (secretion-cells) which are 
separated from one another not by a firm but by a fluid inter- 
cellular substance. When such a hair-cell is moistened with water, 
imbibition takes place through the external wall, and the inter- 
cellular matter gets difi'used, the more remote portions becoming 
intermingled with the more central. The process may be watched 
for hours, and the streams seen to set out, until at length the 
delicate diosmotic and, doubtless, assimilating membrane of the 
endogenous cell-wall becomes destroyed by the excessive im- 
bibition of the water. 
From this object, therefore, the physiologist might satisfy his 
problem of explaining the vital phenomena of the organism from 
its structure and from the physical and chemical changes taking 
place in it, without being compelled to have recourse to an in- 
herent contractility not referable to these factors. The rotation 
the Development of the Organic Cell. It 
of the cell -juices appears to be a mere phenomenon of diffusion, 
— endosmosis co-operating on the one hand, and the property of 
assimilation possessed by the enclosing cell-wall on the other, in 
a continuous act of intermixing the materials concerned. 
Briicke's interesting experiments prove that, as the lightning 
shivers the strong oak, so an excessive electrical current shatters 
the delicate cells within the hairs of Urtica, and puts an end to 
the interesting phenomenon of the circulation of their fluid 
contents. 
If the lower segment of the hair be deprived of its outer coat 
and opened, one or more of the delicate-walled cells which 
occupy this portion swell up and protrude, whilst the rest 
sink down from the apex into the space thus left vacant, and 
occupy it. 
The extruded cells have frequently (PI. I. fig, 3) cellular con- 
tents, not observable in those contained in the naked apical 
portion ; they therefore belong to the category of true tissue- 
cells. 
The circumstance that the integument of actual tissue-cells 
(particularly in the lower animal organisms) is frequently as de- 
licate as the thin walls of the cells found within the hairs of the 
nettle, and that also in other tissue-cells (especially in the sim- 
plest plants) it is so thick, gelatinous, and transparent that it is 
difficult to trace their boundary, has more than once lately given 
rise to the idea that there may be naked cells (without walls), 
which are only mucous globules. 
In my ' Histological Researches,' before referred to, I have 
enumerated several instances in which apparently deficient cell- 
membranes, notwithstanding their great tenuity, could be re- 
cognized with certainty. 
In this respect the Confervse possess a special interest ; they 
offer peculiarly suitable conditions for making investigations 
respecting the structure and development of the cell, as they 
may be examined under the microscope whilst growth pro- 
ceeds — an advantage unattainable in more complex plants or in 
animals. 
In fact, in many species of these plants, their component 
(tissue-) cells, in the earlier phases of development, are so very 
thin and transparent that they are rendered appreciable only by 
a more attentive observation of the changes in form and position 
of the other and more solid cell-contents. The observer may 
likewise arrive at a more ready acquaintance with the origin and 
growth of cells by the comparative investigation of their develop- 
ment under different conditions of nutrition— experiments and 
observations which are indispensable also to the systematist; for 
a change of the conditions of nutrition alters not only the phe- 
8 Prof. H. Karsten on some Phenomena of 
nomena of the growth of cells, but also frequently the very form 
of the Alga itself, even when this has been accounted a specific 
character. 
The cultivation of Spirogyra has proved to me that this plant, 
when liberally supplied with organic nitrogenous matter, gene- 
rates new cells profusely, but that, if this nourishment be 
withheld, growth is limited to the cell-wall. This observation 
consequently shows that a deficiency of such organic nutritive 
supply promotes the centripetal involution of the cell-wall of 
Spirogyra, which in normal conditions of nutrition does not 
happen. 
On the contrary, by a large supply of organic nitrogenous 
material, the growth of the cell-wall, relatively to the formation 
and evolution of new cells, remains in arrear. The cultivation 
of such species of Spirogyra as S. Hornschuchii shows this. 
The partition-walls (septa) of this plant, under normal conditions 
of development, immediately after their origin produce circular 
folds of a determinate size; and the tissue-cells (joint-cells) only 
proceed to produce new cells, after the septiform circular folds 
nave acquired their normal dimensions. (PI. I. fig. 4 a.) But 
this same species, when richly supplied with nourishment in the 
manner stated, presented in the same individual three, and 
sometimes four, or even five partition-walls, without such circular 
folds, and thus indicated that the thickening and further evolu- 
tion of the cell-wall had been supplanted by an augmented de- 
velopment of cells. 
The accelerated formation and development of new joint- cells was 
accompanied by a considerable increase in the deposit of chloro- 
phyll. The successive spiral coils of this substance, which are nor- 
mally separated from one another by intervals of about twice their 
width, approximated so closely frequently about the middle and at 
the extremities of the cell as to touch, and sometimes to overlap, 
each other at their edges, or, indeed, in their entire width ; the 
spiral band being, relatively to the extension of the cell, dis- 
proportionately elongated (figs. 7 & 8). 
In those instances where the layer of chlorophyll does not 
acquire such an excess above its usual length, its increase will 
nevertheless be indicated by a horizontal coil being substituted 
in place of the normal oblique one, in the centre of the cell, over 
the very delicate nucleus (fig. 4). This coil, at the commence- 
ment of the development of new joint-cells, loses the concave, 
furrowed character of its external surface, becomes pressed 
against the wall of the cell and fixed in its central position, as it 
appears, and as the further course of cell-development proves, 
by the production of the daughter cells, which grow up from 
the two opposite extremities of the cell, and extend themselves 
the Development of the Organic Cell. 9 
towards its middle line. These have, however, as yet such thin 
and delicate walls, that they are not themselves visible, but become 
evident only by the changes they produce in the disposition of 
the layer of chloi'ophyll, and by the action of diosmotic fluids. 
Moreover, the chlorophyll-deposit gravitates towards the centre 
of the cell, in the vicinity of the nuclear cell and the approxi- 
mating ends of the two endogenous cells (figs. 9 & 10). Ac- 
cording as the enlargement of the nuclear cell, the absorption 
of the chlorophyll, or the increase in size of the daughter cells 
prevails at this stage, the subsequent phenomena vary. 
Within the nuclear cell two new cells originate, not by any 
constriction and segmentation of its membrane, but by new 
growth within its fluid contents, the nuclear vesicles of which 
become at the same time absorbed. These facts cannot be more 
readily verified than in the larger species of Spirogyra. (See 
Histological Researches, figs. 83-85.) 
The nuclear cell of S. Hornschuchii and of allied species is so 
delicate and transparent that it cannot usually be clearly demon- 
strated without the addition of iodine (PI. I. fig. 5). And as 
the two daughter cells (fig. 6) contained in it are also only ren- 
dered perceptible by this treatment, this species is therefore not 
suitable for the study of this histological element of the joint- cell. 
The growth of the two daughter cells contained in the nuclear 
cell into new joint-cells, as observed in other Spirogyra, does 
not appear to take place in S. Hornschuchii ; for in this example 
it is only the daughter cells of the secondary cell which consti- 
tute new joint-cells, whilst the daughter cells of the tertiary 
cell (the cell-nucleus) enclosed between septum-building young 
joint-cells, proceed to grow into the little circular folds on the 
partition- wall. 
The hypothesis I first promulgated in Wiegraann^s ^ Archiv ' 
for 1843, on the origin of the cup-shaped circular folds of the 
septa, derives confirmation from the occurrence of such develop- 
mental phases as are seen in fig. 11, which, though, indeed, of 
rare occurrence, are sometimes encounteredj particularly in cul- 
tivated plants. 
In this example the middle portion of the septum pi'ojects in 
the form of a hemisphere from each aspect, instead of two cir- 
cular folds. Between this extreme modification and the usual 
form every intermediate grade may be met with. 
The precipitation of the chlorophyll on the nuclear cell is 
scarcely observable under the ordinary conditions of nutrition and 
development, and is probably connected with a general increase 
in the amount of chlorophyll deposited. 
It not unfrequently occurs that three daughter cells are simul- 
taneously developed in a single joint-cell of Spirogyra. In the 
10 Prof. H. Karsten on some Phenomena of 
joint-cells of S. nitida it is most decidedly seen that the new 
partition-walls are not produced by a fold of the membrane of 
the parent cell ; for the several chlorophyll-laminse or bands 
which are present, and completely coherent or continuous at 
first, overlie the septum which originates from the mutual ap- 
position of the endogenous cells (fig. 13). 
In fig. 15, a cell of S. orthospira is represented, in which the 
two daughter cells, a, a (covered by slender chlorophyll-vesicles, 
within the secondary cell b, which has been cautiously detached 
by diosmosis from the primary cell, by the addition of a weak 
solution of chloride of calcium), are in process of forming a new 
septum between themselves, and having the nuclear cell inter- 
posed. The formation of folds from the secondary cell (primor- 
dial sac) is evidently here not the cause of the septum in exist- 
ence, though it be still incomplete with reference to the parent 
cell. 
Fig. 16 exhibits the following stage of development of a joint- 
cell of the same individual, in which neither the two daughter 
cells nor the secondary cells could be detached by the same 
reagent from the wall of the mother cell, although the secondary 
cells of the daughter cells have become separated from the coats 
of their primary cells. These latter formed the still extremely 
delicate septum which divides the cavity of the mother cell into 
two portions. The secretory materials (chlorophyll, starch, &c.) 
are in this stage already enclosed within the secondary cells of 
the daughter cells, whilst in the previous phase, represented in 
fig. 15, they are still found within the secondary cells of the 
parent cell. 
The process of absorption of the chlorophyll-vesicles contained 
within the mother cell, and their reproduction in the daughter 
cells, may be detected in this genus of plants, although not in 
its details ; but in (Edogonium I have witnessed this process after 
the origin of new joint-cells. 
These at first exceedingly delicate partition-walls, developed 
in a normal manner, can scarcely be confounded with the cen- 
tripetal circular folds which the cell-membrane of badly nou- 
rished Confervse, particularly Cladophora and SpirogyrcE, not un- 
frequently produce ; for these latter are much thicker, and their 
central edge always rounded, as is shown in figs. 12 & 14. In 
these examples, the membrane of the secondary cell which was 
detached from the thickened wall of the primary, as a result of 
diosmosis, at the constricted part at x, and which, during the 
operation of the reagent, was disturbed from its position, was 
free from chlorophyll. This nitrogenous secretory matter could 
not, from the deficiency of suitable nutritive material, develope 
itself proportionately with the growing cell-membrane, and. 
the Development of the Organic Cell. 11 
probably also from this same defect in the supply of nitrogenous 
substance from without, was absorbed by the more actively 
assimilating membrane of the fold. 
In S. nitida I have observed such cii'cular folds for fourteen 
days together, without being able to detect a further enlarge- 
ment of them ; and I can give so much the less credence to 
the hypothesis that septa and cells originate from these folds, as 
I have noticed similar circular folds in Cladophora glomerata 
lasting for a period of three months without any change in their 
central aperture taking place. 
Further, I have not only observed, in Cladophora, the new 
joint-cells, in certain exceptional cases, take on such a develop- 
ment as to present two free endogenous cells dividing in the 
cavity of the mother cell (as in cork-cells, in Spirogyj-a, and 
(Edogonium: see my 'Histological Researches,' figs. 21-29), 
but I have also seen, in the plant in question, that the thick 
membranous folds intervening between the two daughter cells 
grow gradually thinner and become finally absorbed. In Sph'o- 
gyra, moreover, I have also witnessed the absorption of the 
membrane of the secondary mother cell, which has subsided, 
along with the chlorophyll-vesicles connected with it, towards 
the conjoined ends of two slowly growing joint-cells, and has 
there become included in the septum produced, and assumed 
the form of an elevation or fold. (Histological Researches, 
p. 63.) 
From the analogy of these occurrences, it may be assumed 
that even the folds represented in figs. 12 and 14 would become 
absorbed by the neighbouring cells, if these last were restored 
to a vigorous and normal state of nutrition, which might in all 
probability be eflfected, where atrophy had not too far advanced, 
by the cautious supply of organic nutritive matter. 
Fig. 19 exhibits a specimen of Cladophora glomerata, in which 
one of the two daughter cells, during the absorption of the 
secreted matters by the fold, has penetrated this last in the 
course of its growth, come into contact with its sister cell, and 
thus established a new septum. 
In the same plant (fig. 18) a thick fold has formed a boundary 
between the two new daughter cells, and so created an obstacle 
to their coming into apposition. In the centre of the fold a 
large corpuscle, like a starch-globule, remains unabsorbed by 
the daughter cells which did not touch it. It would seem that, 
in this example, the very thick circular fold of the mother cell 
has prevented the formation of a septum by the daughter cells. 
A careful examination of Cladophora is sufficient to convince 
any one who might regard an appeal to analogy, even in allied 
plants, as inadmissible, that though an endogenous cell-growth 
12 Prof. H. Karsten on the Development of the Organic Cell, 
is often difficult to discover in this plant, yet such is the fact; 
whilst the majority of naturalists, without it, acknowledging the 
general application of the law of analogy, will not suppose that, 
in the simplest processes of organization, nature follows totally 
different courses. 
The primitive form which matter capable of organization 
assumes is that of the vesicle — the cell, inseparably composed 
of membrane (wall) and contents. Each of these two consti- 
tuents of the elementary organ, constantly exerting the most 
intimate influences upon each other, is capable of advancing 
further in its development by the aid of the physico-chemical 
forces to which it is indebted for its existence. 
The membrane of the cell grows, but not by passive exten- 
sion as a consequence of endosmose of its fluid contents. It is 
rather itself engaged in a constant, although, in fact, almost 
imperceptible, change of the quantity and nature of the matter 
composing it, assuming peculiar forms, very probably dependent 
upon the nature of this material, as I have in some measure 
shown in the preceding pages and in several other contributions. 
The fluid contents of the cell have also their own peculiar 
powers of development. Whilst the cell-wall shows this by its 
enlargement, and usually laminated thickening, the fluid con- 
tents manifest it by the production in them of secretion-cells, of 
transient duration. 
Indeed, as the assimilative faculty of the cell-wall gives rise to 
the formation of progressively higher combinations, the soluble 
products of which become finally dissolved in the general 
nutritive fluid, so, by the agency of the same faculty, secre- 
tion-cells make their appearance in the fluid contents of tissue- 
cells at certain periods of their development. These transient 
secretion-cells serve for the maintenance of the cells of a 
secondary, tertiary, and succeeding generation, which originate 
in the cell-juices, are developed at the cost of the absorbed 
secreted matters, and serve for the reparation of the primary 
cell and the maintenance of the cell-individual. This formative 
process within the cell is not restricted, under certain con- 
ditions of nutrition, to the regeneration of the individual cell, 
but from the cell-contents rich in formative material several 
new cells, of the nature of the reproducing mother cell, are 
simultaneously produced, having for their object the multiplica- 
tion of the tissue-cells. 
Owing to this complicated structure of the tissue-cells which 
enter into the composition of developed organisms, it is erroneous 
to speak of unicellular plants and animals. With as little 
i-eason can we imagine cells without membranes ; such bodies, 
in my opinion, should be designated drops or granules.