M. Mohl on the Growth of Cell-Membrane. 261 
seemed the most probable. Although I shot many in order to 
procure a female, I only succeeded in getting the one above-no- 
ticed, which however I cannot with certainty pronounce to be 
one. It was shot down from a half-finished nest at more than 
twenty yards high. Two or three nests are often attached to the 
same leaf, and twenty or thirty in the same palm. In the be- 
ginning of May the newly-hatched young were obtained from a 
nest, and three quite white eggs from another, although many 
nests were scarcely half- built. 
The notes near the nests were like the warbling and call-notes 
of the linnet. No song was heard. In the stomach only rice- 
grains were found, which they were seen to pluck while hopping 
about the cottages, like sparrows with us. The Bengalese name 
is Bawee (the w sounded as in English). 
[To be continued.] 
XXVIII.— On the Growth of Cell-Membrane. 
By Hugo v. Mohl*. 
[Continued from p. 155.] 
When we compare the conclusions necessarily resulting from 
these calculations with Harting's theory, we see that they are 
decidedly opposed to it. We have good grounds for the assump- 
tion that the mean number, derived from the measurement of 
ten rows of cells, indicates with tolerable accuracy the course of 
the normal development of the wood-cells of Hoya carnosa, since 
the mean numbers already derived from the measurement of 
five rows of cells differ but very slightly from those above men- 
tioned. If we assume this, it follows that the nearer the inter- 
mediate (mittlere) wood-cell (if I may so express myself) of this 
plant approaches the margin of the wood in consequence of the 
progressive conversion of the inner cambium-cells into wood- 
cells, the more it enlarges in the radial direction, so that its dia- 
meter is T ^2 of a millimetre when it lies in the second row of 
cambium-cells (counted from the wood), and when it has advanced 
to the inner row, bordering the wood, the diameter is increased 
to g l Q of a millimetre. According to Harting's view, the cavity of 
the cell will continue of this sizef, since in his opinion the con- 
* From the ' Botanische Zeitung,' May 29th and June 5th, 1816. Trans- 
lated by Arthur Henfrey, F.L.S. &c. 
f I here take the diameter of the cavity of the cell as equalling the dia- 
meter of the whole cell, which is not altogether right, but deviates little from 
the truth, since the cambium-cells of Hoya carnosa have very thin walls, and 
as these walls are double, only half this thickness should be reckoned. This 
is so small a size and one so difficult to give accurately that 1 thought it might 
be disregarded; in a measurement which however cannot claim strict ac- 
262 M. Mohl on the Growth of Cell- Membrane. 
version of the cambium-cell into a wood- cell depends on the de- 
position, of secondary layers upon the outside of the cell; or 
rather, as was shown above, the cavity of the cell must enlarge 
in the radial direction in consequence of this external addition 
of secondary membranes. If we compare with this the size of 
our intermediate wood-cell, the hypothesis cannot be brought into 
agreement with its dimensions, for the cavity of the cell lying in 
the outermost circle of wood diminishes from ■£$ to T y ¥ of a mil- 
limetre, while the total diameter of the cell increases to 7 y. These 
calculations prove beyond a doubt, that in the conversion of a 
cambium -cell into a wood-cell the cavity is far from remaining of 
the same size or enlarging ; on the contrary, it becomes very ma- 
nifestly smaller : this can only be accounted for by a deposition of 
secondary layers on the inside of the primary membrane, or by 
the assumption of the occurrence of an external compression of 
the cell-membrane on every side, causing it to occupy a smaller 
space, for which process no analogy is to be found throughout all 
vegetable anatomy. That the total diameter of the cell distinctly 
increases (from ■§■$ to 7 j millim.), while at the same time the ca- 
vity becomes smaller, is not in the least an objection to the hy- 
pothesis that a deposition of secondary layers takes place in the 
interior of the cell, because there .is no reason to prevent our as- 
suming that an elementary organ may increase in breadth, by the 
intus-susception of new organic matter between the molecules of 
which its membranes consist, during the deposition of secondary 
membranes. That such a growth is possible and actually does 
take place, convincing proof is offered by the spiral vessels situated 
in the interior of the vascular bundle, the spiral fibre of which 
every one certainly considers as a secondary deposit. This en- 
largement of the whole cell does not yet attain its maximum 
while it lies in the most external row of the wood-cells ; the above 
measurements show that in the wood-cells of the second circle the 
total diameter had increased from 7 j to y T , the cavity from T y^ 
to T ^ of a millimetre. As seen by these numbers, the total 
diameter of the cell has increased in a greater proportion than 
the diameter of the cavity, whence the inference, that simulta- 
neously with the enlargement of the cell, a thickening of its 
walls takes place, which however is not quite sufficient to hinder 
the enlargement of the cavity of the cell, by the expansion of the 
cell- wall. 
If from this refutation of the reasons adduced by Harting in 
favour of the external addition of the secondary layers, founded 
on micrometrical measurements, we pass to an anatomical exa- 
curacy, the thickness of the walls parallel with the wood of the cambium- 
cells of* Hoya amounted to at all events not more than ^Vtf of a millimetre, 
if anything less. 
M. Mohl on the Growth of Cell-Membrane. 263 
mination of the wood-cells themselves, their structure affords 
decided proof, that secondary layers are deposited upon the 
inside of the primary membrane. The analogy between the 
structure of the wood-cells and that of parenchymatous cells, 
as for instance the cells of horny albumen, the dotted, thick- 
walled medulla- and bark-cells of Hoya carnosa, in which Hart- 
ing himself does not deny an internal growth, at once offer rea- 
sons not to be disregarded, for the assumption of an analogous 
process of development in the two kinds of cells. Where the 
anatomical relations of the individual layers are so perfectly 
analogous, it would require very clearly-ascertained facts to in- 
duce us to assume that nature follows a different law of formation 
in the wood-cells from that which obtains in the parenchymatous 
cells, and of such facts I have no knowledge. On the other hand, 
the history of the development of prosenchymatous cells affords in 
my opinion very certain evidence of the contrary. In relation to 
this perhaps there is nothing so instructive as the examination of 
the cells of the Conifer -a, and I believe that a conclusion deduced 
from these elementary organs will hold good in reference to the 
wood-cells of Dicotyledons, since spiral fibres on the inner sur- 
face of the cell, together with a bordered dot, resembling those 
occurring in Taxus, are also found in many wood-cells, as for in- 
stance in Viburnum Lantana. Now the examination of young 
shoots of Pinus sylvestris (and exactly in a similar manner also, 
the examination of young dotted vessels of dicotyledonous wood) 
affords evidence that the cavity which subsequently forms the 
border of the dot, and which is situated between the outer closed 
membranes of two contiguous cells, appears very early, while the 
cell-membrane is yet very thin, and is in every case already per- 
fectly formed at a period when no trace can be seen of the dot, 
leading to the cavity, situated in the inner layer of the cell. It 
does not admit of the slightest doubt therefore, that the outer 
closed membrane of the cell is the primary, and that the inner 
layers which are perforated by the canals of the dots are subse- 
quently deposited upon the inner surface of the primary mem- 
brane. 
It is not here meant to be denied that deposits do occur upon 
the outer side of the primary membrane in many cases, for in- 
stance in this very wood of Pinus sylvestris. This takes place in 
the intercellular passages which are found between the cells while 
their walls are still thin, m which an intercellular substance is 
deposited ; but this has nothing to do with the thickening or 
growth of the cell-membrane. 
Although in the foregoing remarks, I have been forced, in the 
defence of my theory, to repel many of the objections advanced 
by Harting and Mulder on anatomical grounds, because I cannot 
264 M. Mohl on the Growth of Cell-Membrane. 
acknowledge as accurate the observations upon which they are 
founded, it is otherwise with the objections which those ob- 
servers have brought forward in a chemical point of view, since 
I do not indeed differ from them as to the facts they mention, 
but cannot agree with the conclusions they have thence drawn. 
Although Harting and Mulder are not themselves always of 
the same opinion in reference to the chemical constitution of the 
compounds found in the cell-wall, yet in regard to the history of 
development of the cell-wall they draw similar conclusions from 
their joint investigations, so that I can here take their objections 
together. The most important points coming under consideration 
are the following : — 
The wall of young cells consists in general of cellulose alone, it 
being coloured blue by iodine and sulphuric acid ; in older cells 
on the contrary, which possess thickened walls, distinct layers may 
usually be distinguished, differing chemically. In the wood-cells, 
bark-cells and milk-vessels, the outermost layer {external wood- 
membrane of Mulder ; cuticle of the wood-cell of Harting) consists 
of a substance wholly insoluble in sulphuric acid. That this 
membrane is produced after that which is composed of cellulose, 
is evident from the circumstance that the young wood- cells ac- 
quire the blue colour in every part ; the outer membrane is there- 
fore considered by Harting and Mulder as a layer deposited on 
the outside of the membrane composed of cellulose. From the 
relation of this outer membrane to the first-formed pores, Hart- 
ing derives the variations of the canals of the dots : when the 
outer membrane is produced in proportionately more abundant 
quantity and spreads itself between two cells, over their whole 
surface, the pores become closed ; if, on the contrary, this mem- 
brane be only deposited in the same proportion as the cells in- 
crease in breadth, the pores remain open ; if, lastly, its develop- 
ment do not keep pace with the expansion of the cell, a cavity 
is produced between the dots. From the circumstance that 
in the full-grown cell the layer of cell-membrane surrounded 
by this outer membrane is usually no longer coloured blue by 
iodine and sulphuric acid, but this colour, even when it appears 
at all, is only to be found in the inmost layer bordering the ca- 
vity of the cell, while the remaining portion is coloured either 
yellow or green, it is further deduced, that these intermediate 
layers of the cell (Mulder's intermediate ligneous substance), which 
take a yellow colour with the reagents mentioned and are soluble 
in stronger sulphuric acid, have been deposited, at the same time 
as the outermost layer, in the direction from within outwards. 
Mulder's and Harting' s views however do not wholly agree in 
reference to the formation of this layer. The former assumes, 
that either the cellulose is wholly absorbed and becomes replaced 
M. Mohl on the Growth of Cell-Membrane. 265 
by this intermediate ligneous substance, or that the intermediate 
ligneous substance is deposited on the outside of the oldest and 
innermost layer (the cellulose) ; while Harting assumes that this 
encrusting matter does not replace the cellulose, but permeates the 
cell-wall composed of cellulose from within outwards and accumu- 
lates in preference in its outer layers. This intermediate ligneous 
substance is always combined with proteine. As analogous to 
this deposition of intermediate ligneous substance, as the inter- 
mediate layers of wood- and bark-cells and as the outer layer of 
medulla-cells (in which latter Mulder did not find the outer 
ligneous layer), other encrusting matters occur in the cells of 
particular organs, for instance pectose in the so-called Collen- 
chyma, and in the milk-vessels a substance partly isomerous with 
vegetable mucilage, partly with cellulose, in the cells of the horny 
albumen of AlstrGemeria, Iris, Phytekphas, &c. 
The conclusion which Harting and Mulder draw from the che- 
mical facts here mentioned, with regard to the development of 
cell-membrane, goes to establish the opinion, that those layers, 
which in the membrane of a full-grown cell are characterized by 
a peculiar chemical reaction, not yet presented by the membrane 
of young cells, have been formed subsequently to the membrane, 
consisting of cellulose, of the young cell, and that since these 
layers occur on the outside of the full-grown cell (the inmost 
layer of which is composed of cellulose, and therefore corresponds 
to the membrane of the young cell), the cell-membrane has in- 
creased in thickness in consequence of the subsequent deposition 
of layers, differing chemically, from within outwards. 
Let us examine whether these conclusions be not too hasty. 
It does not admit of the slightest doubt, that the chemical com- 
pounds which are coloured yellow by iodine and sulphuric acid, 
and which characterize the outer and intermediate layers of most 
full-grown cells, are of later origin than the cellulose which forms 
the membrane of the young cell. From this fact however it is 
a great leap to the assumption, that these layers, which are com- 
posed of a substance differing from cellulose, are in reference 
to their situation also newly-formed layers, which are wanting 
in young cells. This is quite possible ; but it is also possible, 
that the fact as shown by anatomy is altogether otherwise. 
If we first of all disregard totally the above distinct anatomical 
facts, we may, with quite equal right to that by which an ex- 
ternal formation of a new layer is inferred, guess, that in a layer 
of the cell originally consisting of true cellulose, subsequently, 
and without any alteration of its relations of position, the cel- 
lulose is absorbed and replaced by an essentially different che- 
mical compound ; or that the cellulose remains and a new com- 
pound is deposited between its molecules, and prevents more or 
Ann. $ Mag. N. Hist. Vol xviii. U 
266 M. Mohl on the Growth of Cell- Membrane. 
less completely the reaction of cellulose, which this in its normal 
condition exhibits towards iodine and sulphuric acid. Such 
an infiltration might perhaps occur without visible thickening 
of the layer, either if it were not in very great abundance, or if 
the growth of the membrane in a lateral direction connected 
with development of the cell were to afford space for the deposit 
of a considerable quantity of a foreign compound. In these cases, 
the possibility of which in the first place certainly no one will call 
in question, a layer would indeed be formed altogether new in a 
chemical aspect, but no alteration in anatomical relations would 
appear ; and from this subsequently-resulting chemical transfor- 
mation no conclusion should be drawn as to the order in which 
the different layers of the cell-membrane originate, since these 
metamorphoses may take place quite as readily in the last as in the 
first formed layer*. If we admit the possibility of such a meta- 
morphosis in particular layers, it must also be admitted that the 
chemical reaction of a certain layer affords no sure means by 
which it may be recognised as a peculiar anatomical layer, since 
it may easily be imagined, that in different cells, the layers cor- 
responding to each other in an anatomical point of view may ex- 
hibit a great distinction in regard to their chemical transforma- 
tions. Until well-grounded experience has taught us which of 
the cases, which have here been mentioned as possible, really 
occurs in nature, we can only allow ourselves to be guided in 
the recognition of the different layers and the determination of 
the order in which they make their appearance by their anato- 
mical relations ; and although in very many cases the influence of 
chemical reagents affords an excellent means by which we are 
enabled to distinguish the individual layers of cell-membrane, 
which without this assistance it would be difficult or impossible 
to recognise, yet in availing ourselves of this assistance we must 
keep the anatomical relations constantly in view. 
The consideration of these relations leads one, I believe, to a 
result diametrically opposed to that maintained by Mulder and 
Harting. 
In the next place will come conveniently the question, whether 
the outer wood-membrane is produced out of a cellulose mem- 
brane, or is deposited on the outside of an already formed cell. 
This membrane exhibits the most striking contrast to the mem- 
brane composed of cellulose ; if it can be proved to owe its origin 
to the transformation of a cellulose membrane, the much slighter 
* This is no mere guess, as in the parenchyma-cells of some Fern stems, 
especially of PoJypodium incanum, P. nitidum, the inmost layer of the cell, 
an analogue of their primary membrane, is far richer in a substance coloured 
yellow by iodine than the intermediate layer, and requires a much stronger 
action of sulphuric acid for the production of a blue colour, 
M. Mohl on the Growth of Cell- Membrane. 2G7 
differences which distinguish the secondary cell-membranes from 
true cellulose will appear to us of less consequence. This proof 
however, in my opinion, the outer wood-membrane furnishes 
the most clearly of all. I have already, reasoning on the exami- 
nation of the wood of Pinus sylvesiris, on anatomical grounds, 
shown the outer membrane to be the primary ; chemical exami- 
nation of young cells does not contradict this, since at the time 
when the borders of the dots are already perfectly formed, but 
neither the dots themselves nor the inner layers in which they 
are situated yet exist, the membrane of these cells is coloured 
by iodine and sulphuric acid, not yellow, but blue. The relation 
of the membrane to the borders of the dots leaves no doubt that 
we have here to do with the same membrane which subsequently 
appears as the outer layer of wood with wholly altered chemical 
properties. We must therefore assume, that the cellulose of 
which this membrane originally consists is either absorbed and 
replaced by the substance of the outer ligneous layer, or that 
the latter penetrates into the cellulose and prevents its reaction 
towards iodine and sulphuric acid. Which of these cases occurs, 
cannot be decided until some solvent for the substance of this 
membrane shall be found which will not at the same time dis- 
solve the cellulose, yet remaining in it, or at least will give some 
evidence of its presence. Since such a solvent is not yet known, 
the question must for the present remain open ; perhaps the fol- 
lowing observations may afford a hint. 
I tried next whether the action of stronger sulphuric acid on 
the outermost layer of membrane of the wood-cell, especially in 
the Conifera, would produce a blue colour, but did not in this 
way attain my object. The formation of the blue colour de- 
pends therefore on the simultaneous reaction of sulphuric acid, 
iodine, water and cellulose. If concentrated sulphuric acid be 
applied, the cell-membranes do not become blue so long as the 
necessary water is wanting ; or if they be already coloured blue, 
this colour is soon lost again, and the secondary layers become 
dissolved. This solution however affords no convenient means 
by which to obtain the outer membrane isolated, and to examine 
the colour which, after the action of a stronger acid, it assumes 
with iodine and weak acid, since so soon as water and tincture of 
iodine are added to the fluid in which the preparation lies, the 
dissolved cellulose is precipitated again of a very dark blue co- 
lour, and envelopes the outer membranes in such a manner, that 
no certain conclusions can be drawn as to its colour. I sought 
therefore to separate the outer membrane from the secondary 
layers before I applied the sulphuric acid to it. This may always 
be done in the fibres of the liber of the black fibrous wood of the 
Palm which is imported from Brazil for the manufacture of sticks. 
U3 
268 M. Mohl on the Growth of Cell-Membrane. 
&c, as the liber-cells may easily be detached from each other if 
the vascular bundles have been kept for some time in dilute ni- 
tric acid, by which means the outer membranes of the contiguous 
cells are not separated from each other, but from the secondary 
membranes, and may be obtained isolated in large pieces. With 
iodine and sulphuric acid of a degree of concentration which 
does not dissolve the secondary membranes, but colours them 
bright blue, this outer membrane behaves exactly like the outer 
membrane of the wood-cells of dicotyledons, that is, it does not 
swell up, but acquires a dark yellow colour. If we apply stronger 
sulphuric acid, capable of completely dissolving the secondary 
layers, the outer membrane, without any perceptible expansion, 
acquires either an intense greenish or tolerably pure blue colour. 
This contains cellulose also, but in what I may call a much more 
strongly combined condition than is the case in the secondary 
layers, so that not only is a far stronger acid necessary to bring- 
out the blue colour, but the cellulose present in this membrane 
is also protected from solution. This greater resistance to the 
action of sulphuric acid clearly can only depend upon the pre- 
sence of the substance which acquires the yellow colour with 
iodine and sulphuric acid. This resistance however has a certain 
limit,. since this membrane is soluble in more concentrated sul- 
phuric acid. It differs therefore in reference to this last circum- 
stance from the outer membrane of the wood-cells of dicotyledons, 
which resists the action even of the more concentrated sul- 
phuric acid. To try therefore whether cellulose might not be 
discovered in the latter by the action of a stronger acid, I sub- 
mitted the wood-cells of various Conifer a, particularly of Pinus 
sylvestris, to a similar treatment with nitric acid, &c. The ex- 
periment succeeded but imperfectly. After the action of a strong 
acid, the outer membrane exhibited throughout a greenish co- 
lour, but the development of the blue colour was so weak, that 
I remained in doubt whether it was actually situated in the outer 
membrane itself, or whether possibly it was not to be ascribed to 
a thin layer of adhering cellulose. I place no weight therefore 
on this experiment, and mention it here chiefly to invite others 
to direct their attention also to this point. 
The following observations made on Ferns appear to me to 
bear more importantly upon the theory of the development of 
cell-membrane : — The brown cells which in Ferns form the layer 
by which the vascular bundles are surrounded, withstand the ac- 
tion of sulphuric acid as obstinately as perhaps any other vege- 
table tissue. In many Ferns all the walls of these cells do not 
possess a brown colour, but merely those portions of the walls 
lying upon the vascular bundle, or these and the side walls, 
while the side turned away from the vascular bundle is unco- 
M. Mohl on the Growth of Cell-Membrane. 269 
loured, and reacts like cellulose with iodine and sulphuric acid. 
The brown-coloured walls are usually much thicker than those 
consisting of cellulose. Leaving the brown colour out of view, 
these cells correspond exactly, in respect to form and their be- 
haviour toward iodine and sulphuric acid, with the epidermis- 
cells of many leaves. Similar cells occur in the parenchyma of 
the stem of Polypodium nitidum, Kaulf, some isolated, some in 
groups of three or four, scattered among the parenchyma-cells, 
which are usually composed of cellulose ; in these cells also one 
wall is generally thinner and formed of cellulose, while the re- 
maining walls are very thick and brown, and withstand sulphuric 
acid. All sides of these cells are finely dotted, as is also the 
case in the cells of the brown coat inclosing the vascular bun- 
dle ; the dots penetrate as well in the thickened brown as in the 
thin walls, from within outward to the thin outer and imperfo- 
rate membrane, which membrane possesses the same chemical 
peculiarities as the secondary layers lying behind it ; that is to say, 
it consists sometimes of cellulose, at others of a substance with- 
standing sulphuric acid. Now I found, both among the cells 
scattered in the parenchyma and in the brown layer inclosing 
the vascular bundle, particular cells, which certainly, in reference 
to their form, though not in regard to their chemical characters, 
wholly agreed with neighbouring brown cells, in which therefore 
one wall was also thin and the rest considerably thickened. In 
some parts all the walls of these cells, both thick and thin, con- 
sisted of cellulose ; in other parts the thickened walls were only 
composed of the brown substance in one point, while the remain- 
ing portion, transversely through the whole thickness of the cell- 
wall, consisted of cellulose ; the line of demarcation between the 
brown and the uncoloured portions was riot distinctly defined. 
From the piecemeal composition of the cell- walls of tracts formed 
of cellulose, and others consisting of brown substance, it clearly 
results that the greater thickness which the brown walls of these 
cells usually possess, compared with the walls consisting of cel- 
lulose, is neither to be ascribed to the deposition of membranes 
upon the outside of the young cellulose membrane, nor to the 
interposition of a considerable mass of brown substance between 
the molecules of the cellulose, since if the formation of the thick- 
ened brown walls depended on these causes, the portions con- 
sisting of cellulose could not have exhibited the same thickness 
and form as the coloured portions in the only partially brown- 
coloured cell-walls. The reason of the brown colour therefore, 
and of the altered chemical behaviour, must be looked for in a 
transformation of the whole substance leaving the form and or- 
ganization of the cell-wall unchanged, or in the infiltration of a 
270 M. Mohl on the Growth of Cell-Membrane. 
foreign matter in a quantity very small in proportion to the cel- 
lulose. 
I thought it necessary to enter more minutely into the de- 
scription of these cells, because they offer the clearest evidence 
that the presence of a compound differing chemically from cel- 
lulose in a thickened cell-wall, even when traces of cellulose can 
no longer be detected in the membrane by iodine and sulphuric 
acid, affords no sufficient ground for the assumption that the 
thickening of the wall depends on the deposition of an incrust- 
ing substance, and that we have to regard those portions of the 
cell-wall formed of this substance as produced subsequently to 
the portions which are composed of cellulose. Were the in- 
crusting substance, situated at particular points, to penetrate 
through the whole cell-wall (primary and secondary membrane) 
in these cells, the extent to which it spread would include the 
outer layer of the cells, so that this layer would possess all the 
peculiarities of the outer wood-membrane, and it would thus ex- 
actly fit all the conclusions respecting this membrane which 
Mulder and Harting have drawn ; on the other hand, it is not 
necessary to indicate more minutely how false would be the as- 
sumption of its originating subsequently. 
The organization of the above-described cells of Polypodium 
nitidum appears to me to be of importance in so far as it is capable 
of warranting our conclusions as to the structure of epidermis- cells 
and cuticle, which corresponds with it exactly in an anatomical 
point of view. Some years since* I stated the anatomical grounds 
which prevented my regarding the cuticle as a layer secreted upon 
the outside of the epidermis-cells, and which testified that it con- 
sists of the thickened outer walls, and partly also of the side walls 
of the epidermis-cells, the substance of which has become capable 
of resisting sulphuric acid in consequence of a peculiar metamor- 
phosis. This explanation does not appear to have met with a fa- 
vourable reception, but renewed researches have caused me to per- 
severe in iry view, and it appears to me to be especially proved by 
such cases as where the cuticle of canals of dots is continued out 
from the cavity of the epidermis-cell (as in the leaves of Hakea 
gibbosa), or where the side walls of the epidermis-cells are dotted 
and possess the same chemical peculiarities as the cuticle {e.g. in 
Hakea gibbosa, H. pachyphylla, Hoy a carnosa), where also un- 
doubted primary and secondary membranes in a similar manner 
exhibit the chemical characters of the outer wood-membrane; 
lastly, such cases as where the primary membrane of the side wall 
in that half which is directed toward the upper surface of the leaf 
* Linnaea, 1. 10, Verm. Schriften, 260. 
M. Mohl on the Growth of Cell-Membrane. 271 
possesses the chemical peculiarities of cuticle, and that half, on 
the other hand, which is contiguous to the parenchyma of the 
leaf, the characters of cellulose {e.g. in Hoya carnosa, Aloe obliqua, 
margaritifera) . In all these cases cells present themselves to us, 
the walls of which, either in certain situations or throughout their 
whole extent, withstand sulphuric acid, and in which no cellulose 
is to be discovered. The analogy which exists between these cells 
and the above- described cells of Polypodium nitidum appears to 
me to be of importance to the explanation of these latter circum- 
stances. If it be certain in these last, that their membranes, not- 
withstanding that no cellulose is any longer to be demonstrated 
in them, nevertheless have their origin from a cellulose layer 
which exhibits exactly the same organization and thickness as the 
incrusting membrane, and in many cases still forms particular parts 
of the membrane, not even then must the conclusion be drawn 
in respect to the cuticle from its chemical constitution, that it is 
a layer secreted upon the upper surface of the epidermis-cells, 
until it can be demonstrated that this theory is in accordance 
with the anatomical phenomena, and that the instances I have 
given of a composition of cuticle from cell-membranes, and of the 
occurrence of epidermis-cells with side walls, partly consisting of 
cellulose and partly of the substance of cuticle, are founded upon 
false observations. 
Whether now in these cases the cellulose is partly or wholly 
absorbed and replaced by the incrusting matter, or whether its 
reaction to iodine and sulphuric acid is merely prevented by the 
latter, is uncertain. It appears however to me not improbable 
that the latter is the true view, since the assumption that in- 
crusting substance coloured yellow by iodine and sulphuric acid at 
least to a certain degree interferes with the known reaction of cel- 
lulose, supported not only by the above-mentioned behaviour of 
the outer layer of the liber fibres of a Palm and of the wood-cells 
of Pinus sylvestris, but also by the behaviour of the secondary 
layers in almost all full-grown wood- and parenchyma-cells. 
Young cells, for instance the pith of a young shoot of Sambucus 
nigra, the cambium-cells of dicotyledons, &c, become coloured 
bright blue by the application of a very dilute acid, while the 
medulla-cells of a full-grown branch of Sambucus and the perfect 
wood-cells, treated with the same acid, only develope a yellow 
colour and require it much more concentrated, and then as deep 
a blue colour is not produced, on account of the yellow colour of 
the incrusting matter mixing with and rendering it green. A 
bright and intense blue colour can usually only be obtained in 
the secondary layers of full-grown wood-cells when so strong an 
acid is employed that they do not merely swell up but are par- 
272 Bibliographical Notices. 
tially dissolved ; in this case the dissolved portion is precipitated 
in combination with iodine, if the acid be diluted with water, of 
a splendid and intense blue colour, while the portion of the mem- 
brane, the organic structure of which has not been destroyed, 
although it has undergone a considerable breaking up, exhibits 
the blue colour but weakly in proportion, and frequently appears 
green on account of the preponderating intensity of the yellow 
colour. Since in this manner a perfect destruction of the orga- 
nization of the secondary incrusting layers renders it possible for 
the reaction of cellulose toward iodine and sulphuric acid to ma- 
nifest itself, it is certainly conceivable that in cases where the sul- 
phuric acid is not in a condition to affect a membrane, cellulose 
may be present in it, but be protected from the action of the acid 
by the incrusting matter, and thus rendered imperceptible. 
BIBLIOGRAPHICAL NOTICES. 
Palceontographica : Beitriige zur Natiirgeschichte der Vorwelt. Heraus- 
gegeben von Dr.W. Dunker und Herm. von Meyer. 1 Band, 
1 Lieferung. — Palceontographica : Contributions to the Natural His- 
tory of the Antediluvian JEra. Edited by Dr. William Dunker 
and Hermann von Meyer. Vol. i. part 1. 4to. 44 pp. and six 
plates. 
Under this title the editors intend giving full descriptions of re- 
markable fossils hitherto unpublished, illustrated by accurate and 
highly finished plates. The first part contains: 1. A description 
of a new species of Pterodactylus, Pt. Gemmingii, by Hermann von 
Meyer, followed by a synoptical table of all the sixteen species 
hitherto known of that highly interesting genus of flying Saurians. 
2. A description of Aspidura Ludenii, by Friedrich von Hagenow, — a 
very curious species of QphiuridcE found in the " Muschelkalk " near 
Jena. 3. A description of a superb palate of Myliobatis Testa, new 
species, from Sicily ; of Tornatella abbreviata, new species from the 
Gosau formation; and two teeth of Squalidce, found near Cassel. 
4. A description of Omphalomela scabra, a fossil trunk of a plant found 
in the limestone banks of the Keuper formation near Kolleda in Thu- 
ringia, by Professor Germar. 5. Description of several new plants 
from the copper- slate formation of Richelsdorf, by J. Althaus, with 
a synopsis of all the plants hitherto met with in that formation. 
6. Descriptions of several new species of shells, partly marine, partly 
fluviatile, recently discovered near Halberstadt in a sandstone be- 
longing to the lias formation, and highly remarkable from their per- 
fect preservation, which allows in many cases of their colours being 
recognised. 7. Enumeration of the fossil shells occurring in the ter- 
tiary formation of Magdeburg, by Dr. Philippi.