M. J. (Matthias Jacob) Schleiden.

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a is a stinging hair, with a knob, and circulating fluid in the interior ; 6, a club-shaped
glandular hair. Every one of the simple cylindrical cells, which, placed one upon the
other, form the stalk, exhibit a cytoblast and circulation. The knob, formed out of
many little cells, is covered with secreted resin. The arrows show the direction of the
streams.

93 A prickle-hair from the leaf of Dipsacut fullonum. It consists of a long, some-
what bent cell, thickened by layers (a), which is embraced at the base by an elevated
mass of porous epidermis-cells.



78 ON THE PLANT-CELL.

of the epidermal processes are the stinging hairs. They constitute
the type of a very common form of the epidermal tissue, in which a
few wart-like cells are elevated above the surface, and embrace the base
of a single elongated cell (figs. 92, 93. a).

Such hairs, very much thickened and distinguished by the porosity
of the epidermal cells, are seen in Dipsacus (fig. 93.); ordinarily
the lower cells of such hairs are swollen, with thin walls, whilst those
above are pointed and thick-walled. They are frequently marked on
the upper surface with little warts spirally arranged, and with elevated
stripes. This form characterises the Urticacece, the Boraginacece, the
Cucurbitacece, and the Loasacece. The mechanism also of the stinging
hairs in Urtica, Wigandia urens, and the Loasacece, is very interesting.
Almost all stinging hairs end in a little knob-shaped swelling, which
is exceedingly brittle, and easily knocked off by a touch. The opened
point, on being pressed against, exudes the secretions contained in the
cells at the base of the hair, and will produce poisonous effects when
introduced into animal tissues. Our indigenous nettles are the least
injurious. The stings of the Loasacece are much more so, while the Urtica
crenata and crenulata of the East Indies produce wounds in which
pain is felt for weeks and months after touching them. The most dan-
gerous of all is the Urtica urentissima of Blume, called in Timor Daoun
setan, and by the English " Devil's leaf." The wounds of this plant give
pain for years after, especially in damp weather, and occasionally death
from tetanus is the result. Could we separate this poison, it would be
the most powerful vegetable poison known.

In the early stages of growth these hairs, all of them, possess an active
circulation of the sap. Some hairs have their contents absorbed at a
special time, so that the hair is, as it were, absorbed into its own proper
cavity. This remarkable phenomenon
takes place in the hairs of the style in
Campanulacece* (fig. 94.). Also in the
globular cells of knob-shaped hairs, which
then look as if half had been cut through,
or as if a cover had been removed.f
Meyen has published a work on hairs,
distinguished by a host of peculiarities.^

Cork. A peculiar change goes on in
the epidermal cells of particular parts,

more especially the stem and fruits of Jf&l x^nJJ 15""")

certain trees. A quantity of yellow slimy
matter collects in the cells and gradually
increases in quantity, so that the external
cell-wall is torn by the under one and lifted
above the surface. Cells are formed in
a hitherto undiscovered manner in the

yellow substance, which assume the form of four- cornered tables, and are
arranged in connected concentric layers. When perfectly formed, this

* See Brongniart, Ann. de Sc. Nat., 1839, p. 244.

f According to Meyen; but it is erroneous.

j Ueber die Secretionsorgane der Pflanzen. Berlin, 1837.

94 Longitudinal section through the style of a Campanula, with two hairs : a, a hair
exhibiting a circulation ; its point is enclosed in a layer of mucus : b has lost its con-
tents, and is in consequence contracted.




FORM OF THE PLANT-CELL. 79

tissue exhibits great elasticity, and the tissue known by the name of cork
belongs to this form. It exists, however, in countless other forms, and
its existence seems detetermined by the presence of an epidermis which
vegetates for a longer period than is usual. When the process of cork-
formation once commences, it goes on ; but should the layer be thrown off
the tree at any particular stage of its growth, it is not again engendered,
as, for instance, in the vine and the Clematis Vitalba. Mohl * was the
first who accurately examined this subject, and I have sought to explain
its origin, f

Root-sheaths. If the organs of Pathos crassinervis, called aerial-roots,
are examined, there will be found a distinct epidermis, with stomates whose
semilunar cells, filled with a brown granular matter, are elevated above
the surface of the epidermis, and form a special tissue whose walls exhibit
the most delicate spiral fibres. These cells are filled with air, and thus
give the brilliant white appearance to these roots. How this layer origi-
nates is not very clear, but it is formed in the same way at the points of
the roots as in the other parts. The same layer is found on the roots of
most tropical Orchidacece, and the cell-walls exhibit in them the most
striking modifications. It is very remarkable in Aerides odoratum. I have
seen it in Epidendrum elongatum, Cattleya Forbesii, Brassavola cordafa,
Maxillaria atropurpurea, M* Harrisonii, Acropera Loddigesii, Cyrto-
podium speciosissimum, Oncidiunt altissimum, and other species. I also
found it, but without spiral fibres, in Pothos reflexa, acaulis, violacea,
cordata, longifolia, and digitata. In other families I have not seen it.
The roots have ordinarily a fresh green point ; in these the cells are full
of sap, and the green cortical parenchyma is seen through them. The
relations of this layer differ so much from those of the epidermal cells,
that it has been regarded as a peculiar tissue. Link J first discovered
this layer, Meyen examined it more accurately, but no one has correctly
appreciated it.

* Ueber die Entwickelung des Korkes und der Borke. Tub. 1836.
f Beitrage zur Anatomie und Physiologie der Cacteen.
\ Elem. Phil. Bot. Ed. i. p. 393.

Physiologie, i. p. 47. Meyen, copying Link, says that Dutrochet has examined
this tissue ; but this is a mistake.



80 ON THE PLANT-CELL.



CHAPTEE II.

ON THE LIFE OF THE PLANT-CELL.

SECTION I.

FUNCTIONS OF THE INDIVIDUAL CELL.

30. ALL the chemical and physical powers of the earth naturally
act upon the plant-cell. Inasmuch as these striking phenomena are
called forth, and especially as they exhibit, in and through the cell
itself, an especial form of action, I call all such action the life (vita)
of the cell. Most of the physical powers of nature are too little
known for us to be able to comprehend the peculiarities which they
exhibit under especial relations. We can only say generally that
the various chemical processes which take place in the cell must
be accompanied by changes of temperature, electricity, absolute
and specific gravity, &c., without being able to count or measure
the same. There are, therefore, only a few relations which permit
of a more accurate estimation, as the absorption of foreign agents
(endosmosis), the decomposition and recomposition of the same (as-
similation and secretion), the getting rid of superfluous matter
(exhalation and excretion), the working up of the assimilated
matter (organisation), the movements of the contents of the cell
(circulation), the movement of the whole cell (locomotion), the
formation of new cells within the old ones (propagation), and the
cessation of all these processes (death).

I. On the Absorption of Foreign Agents.

31. The cell-membrane (in its young state) is perfectly closed,
but permeable to all fluids. It thus takes up all perfect solutions
through its walls into its cavity. In consequence of the chemical
change going on in its interior, the cell constantly contains a fluid
thicker than water, or dilute solutions of saline substances, and
mostly one which, like a solution of sugar or gum, has so great an
affinity for water, that they draw water into the cavity with a cer-
tain degree of force, and, on the other hand, a small quantity of the
concentrated fluid passes out of the cell. The passing in of the
fluid into the cell has been called by Dutrochet endosmose, and its
passing out exosmose.

The property which cellulose possesses of allowing fluids to pass
through it has already been mentioned. It is an entirely superfluous



LIFE OF THE PLANT-CELL. 81

and gratuitous hypothesis to suppose that it possesses invisible pores, or
that the membrane stands in the same relation to fluid as salts to water.
In the latter case, the water is supposed to dissolve up a little of the mem-
brane, which, in passing through, it yields up again. The passing of the
fluid through the membrane is produced by the relation of water to certain
other substances contained in the cell. If gum or sugar is dissolved in
a small quantity of water, and pure water is poured carefully over the
solution, the two liquids remain apparently for a short time unmixed, but
at the edges where the fluids meet a process goes on, in which the two
fluids pass one into the other until the whole is completely mixed. If the
two fluids are separated by a vegetable or animal membrane, the attraction
is not diminished, because both fluids penetrate the membrane and thus
come in contact, but the thicker fluid passes through the membrane with
more difficulty than the thinner. Thus a larger quantity of the thin fluid,
in the same time, is found present with the thicker than of the thicker with
the thinner. The experiment may be performed in glass tubes, wh<.>n the
relative height to which the fluids will rise in a given time will be in pro-
portion to their relative thickness. The same results take place when
fluids, not thickened, but varying in specific gravity, as alcohol and water,
are employed, the lighter passing into the heavier most rapidly. Dutrochet
called the passing in of the thinner fluid endosmose, and the passing out
of the thicker exosmose, and measured the endosmotic power of the fluids
by the difference of height which they reached in tubes. By means of a
graduated apparatus, Dutrochet estimated the relative power of the fol-
lowing substances as compared with water :

Animal albumen . . at 12
Sugar .... 1J

Gum .... 5-17.

Vegetable albumen belongs to the nitrogenous vegetable substances, and
is similar in many points to animal albumen. In its physical properties
it is difficult, if not impossible, to separate it from the vegetable substance
described above as mucus (protein). It appears to me not too much to
assume that this vegetable albumen (mucus), out of which the cytoblast is
formed, possesses the same endosmotic power as animal albumen. We can
thus easily explain how it is that, immediately after the cytoblast is sur-
rounded by a membrane, endosmose begins, and thus takes up those sub-
stances upon which the cytoblast exercises a changing influence. In this
( way sugar and gum are formed, and the cell is thus filled with substances
which increase the process of endosmose. Scarcely any further explana-
tion of the process of absorption is needed, as this simple process suffices
for the understanding the most complicated phenomena of vegetable life.
It is to be regretted that so few experiments have been made on the
relations exhibited by this process. There are two points of especial im-
portance. The first is, the great variety in the nature of the various sub-
stances within and without the cells of plants, and the great difference in
the power with which they are attracted: on the relation of numerous
solutions to one another, we have no experiments. In the second place,
the nature of the separating membrane demands attention. Water and
alcohol, for instance, exhibit a very powerful reciprocal attraction ; but in
an endosmotic apparatus, when bladder or caoutchouc is used as a means
of separation, the result is very different. With the bladder the water
passes to the alcohol, but not vice versa, as alcohol does not easily per-
meate animal membrane. With the caoutchouc the result is exactly the

G



82 ON THE PLANT-CELL.

reverse, the alcohol readily passing through this substance. Similar
modifications in the simplest processes of cell-life must take place, on
account of the countless varieties of cell-membrane. In all experiments,
however, it is necessary to avoid the the hypothesis of the porosity of the
organic membrane, which can only be attended with the same bad results
as the notion of the existence of atoms in chemistry.*

32. The most universally distributed medium of solution in
nature, water, is also the fluid which is absorbed by the plant-
cell, and conveys all other matters into its interior. The most
essential of these matters are carbonic acid and ammonia, both of
which are contained in water which either falls from the air or haa
been a long time in contact with it. Water, carbonic acid, and
ammonia contain carbon, hydrogen, oxygen, and nitrogen, all of
which are essential to the formation of the assimilated substances
and to the especial nourishment of the cell. But the water occa-
sionally conveys to the cell, in small quantities, all substances which
are capable of solution in water.

In spite of the almost endless works upon the nourishment of plants,
nothing is in a more uncertain state than our knowledge of the food
necessary for plants. This has arisen from the facts having been selected
from, and the experiments made upon, the higher and more complicated
forms of plants instead of the lowest. The simplest and most natural
object for such researches is the Protococcus viridis, or some other simple
Conferva., which consists of one or only a few cells, and which floats free
in water, and contains the substances universally necessary for the life of
the cell. These plants require nothing more for their vegetation than
pure water, which has taken up from the atmosphere carbonic acid and
ammonia, and perhaps a very small quantity of inorganic salts ; the
necessity for which last has not been proved, but is supposed to be
necessary from analogy with the higher plants. The experiment is
easily made of supplying these plants with water containing a large
quantity of carbonic acid, when they will be found to grow more rapidly,
and thrive more luxuriously, than when placed in water to which
humus, humic acid, or humic acid salts have been added. This is
sufficient proof that these last substances are not essential to the life of
the cell.

It is worthy of remark, that just as Carices, and other so-called moor-
plants, flourish with a certain quantity of humic acid, which is generally
unfavourable to vegetation, so also other plants, as the little Conferva
which requires tannin and grows in infusions of galls, require other
substances. The Mycoderma aceti grows under the influence of the
decomposition of vinegar. In these cases, probably, the free acid is as
little necessary to nutrition as in other plants, but the mode and manner
of the decomposition of the acid is a favouring moment for the vegetation
of the above-named plants.

Few researches have been made on the nature of the nitrogenous
substances in the simplest plants. I have hitherto supposed that the
nitrogenous compounds of plants are pure protein. But if we regard

* See Dutrochet, L' Agent immediat du Mouvement vital devoile, &c. Paris, 1826.
Also Poggendorff's Annalen, vol. xi. p. 138., vol. xxviii. p. 134. ; and Schweigger's
Journal, Iviii. p. 1. 20. [Also Draper on the Chemistry of Plants, and Matteucci on
the Physical Phenomena of Living Beings. TRANS.]



LIFE OF THE PLANT-CELL. 83

them as albumen, fibrin, and casein, we must allow for the absorption
of sulphur and phosphorus, as well as salts of sulphuric and phosphoric
acids : through this the phenomena become much more complicated.
The reduction of the phosphates and sulphates to phosphoric and sul-
phuric acids, and the separation of the sulphur or phosphorus and the
oxygen, indicate complicated chemical processes, which are not, however,
performed without the presence of nitrogenous substances, and thus they
appear to be the simplest additions to the plant-cell next the formation
of protein. The notion of such changes is justified by Mulder's re-
searches upon the mother of vinegar (Mycoderma Pers.), which is
formed out of hydrated acetic acid and the albumen contained in the
vinegar. It is composed of cellulose and protein, which always exist in
the proportion of one equivalent of protein with four of cellulose.* A
similar accurate examination of the fermentation-cells would be of the
highest interest.

The plant-cell takes up all substances that are in solution in water,
both mineral and vegetable poisons and tannin, which, by producing an
interruption of the chemical processes, are capable of destroying its life.
The cell in this view has no choice beyond the endosmotic power of the
various substances which are presented to it. \ On the other hand, every
fluid is unfit for the nutrition of the cell, which, on account of its specific
nature as alcohol, or its density as concentrated solutions of sugar and
gum:}:, renders endosmose impossible, should it even contain all the
elements necessary for the growth of the cell.

In the last place we may observe, that in the changes which are
undergone in the cell of the plant there is no individual element, with
the exception of oxygen, which takes part alone in those chemical pro-
cesses. Nitrogen is taken in with water, but passes out again without
undergoing any change. Hence all calculations with regard to the
composition and metamorphoses of organic bodies, in which the pure
elements, and not their combinations, are supposed to play a part, must
be rejected as hypothetical.

II. On the Assimilation of the absorbed Matters, and Secretion.

33. The assimilated substances consist of carbon, hydrogen, oxy-
gen, and nitrogen (sometimes with sulphur and phosphorus) ; and these
are only assimilated from the definite combinations, carbonic acid,
water, and ammonia. As soon as these substances are conducted
into the interior of the cell, in the before-mentioned manner, che-
mical processes originate which first commence in the destruction
of the ammoniacal compounds and (perhaps as a result) the decom-
position of the water, and whose progress is distinguished by the
action of the assimilated nitrogenous matter (mucus) upon non-
nitrogenous substances. Thus are formed at the same time both
mucus and non-nitrogenous substances.

* Liebig's Annalen, vol. xlvi. p. 207.

f See the experiments of Saussure, Chemische Untersuchungen iiber die Vegeta-
tion, Leipzig, 1805, p. 228.

\ De Saussure and Davy found that plants flourished on dilute solutions of gum and
sugar.

Davy, Elements of Agriculture.



84 ON THE PLANT-CELL.

I call those assimilated matters which have been mentioned above in
the chapter on the substances contained in plants. We can only place
in this class those substances which are produced and exist in the
simplest cells, and which are necessary universally for the growth of
the plant- cell. I do not say that those mentioned above are all, as
subsequent researches may add to their number by the discovery of
unsuspected relations. There is, for instance, resin, which, though fre-
quently present, is excluded because we cannot detect its transitions to
the assimilated matters as we can in the fixed oils. In this way we may
draw a permanent and useful distinction between assimilated substances
and secretions. I would, however, disclaim here any analogy that may
be supposed to exist between these substances and those of the animal
kingdom, and must insist on regarding these terms as connected with
ideas belonging to the vegetable kingdom alone.

There can be little doubt that all the foregoing processes of decom-
position and recomposition of the substances of which the plant-cell is
composed have their foundation in well-known chemical powers and laws.
That the elements of which the plant-cell is composed obey the same
laws in the cell as out of it, seems warranted by the strongest presump-
tions of inductive inquiry. All the elements of which plants are com-
posed are derived from the inorganic world, and the combinations which
carbon, hydrogen, oxygen, nitrogen, &c. enter into in the plant take
place under the influence of the properties or powers which they possess
independent of the plant-cell. It is for those who suppose that these
substances undergo some change in passing into the organism to bring
forward some proof of such a change. So long us this proof is wanting
(and it ever will be), we must regard it as true that all the chemical laws
find uncontrolled exercise in the organism. The activity of the modern
school of chemists, Liebig and his followers, Dumas, Mulder, &c., lead
us from another point of view to the same result*. Their labours have
placed the perfect identity of the elements and processes which go on in
and out of the body upon the most satisfactory inductive basis. Liebig
and Mulder especially have shown that, if we analyse the course of
changes which occur in the elements composing an organism according
to the laws of inorganic chemistry, we come to the same results as
though they were independent of the organic body.

The questions to be solved in this department of vegetable physiology
are, first, what are the compounds, and what the chemical processes, by
which the simplest plant-cells are formed ; and, secondly, what are the
compounds, and in what way are formed the substances, which are con-
tained in every plant-cell. For a knowledge of the compounds, am-
monia, carbonic acid gas, and water, which are every where and
universally required for the formation of the assimilated matters, we
are indebted to the chemists, De Saussure, Liebig, and others. Liebig *
has rightly exposed the absurdity of those who attempt to explain all
organic phenomena by what takes place in the elements, away from an
organism. There is, however, one fact which occurs in inorganic bodies
which exercises the most important influence in organic combinations.
It is, that bodies will enter much more freely into union with each other
at the moment they are released from other combinations than at any
other time. A body in this condition is said to be in statu nascenti, in
a nascent state. Of the substances which constitute the food of plants,

* Chemistry in its relation to Physiology and Pathology.



LIFE OF THE PLANT-CELL. 85

two, water and the salts of ammonia, easily enter into a state of decom-
position. Water on coming in contact with zinc gives off its hydrogen,
and the weakest galvanic current serves to separate its oxygen and hy-
drogen ; whilst an alteration of temperature or solution is sufficient to
decompose or produce important alterations in the salts of ammonia.
Thus, through the destruction of a single equivalent of water, an impulse
would be given to an endless chain of chemical processes, which would
result in the development of those substances which are found in the
plant-cell. The question is, however, still unanswered as to what
change is the first that takes place in the series. Liebig has observed,
very correctly, that, as far as the ultimate results are concerned, it
signifies little whether carbonic acid or water is first decomposed. Al-
though, as before stated, we must not explain the changes which take
place in the cell on the supposition that the elements, as such, unite
together, yet, on the other hand, we are not in a position to say that the
formation of starch, &c. is dependent on the decomposition of carbonic
acid and water. Where plants grow, and where cells are formed, there
we have present at the same time water, carbonic acid, and the com-
pounds of ammonia. We also see that nitrogenous and non-nitrogenous
substances are developed at the same time, and apparently by the same
process. In this point of view, the analogy between the composition of
vinegar and the mother of vinegar, which last, according to Mulder,
consists of one equivalent of protein and four equivalents of cellulose,
is a matter of some interest. Thus :

C H O N

74 Water (H O) = . . 74 74

94 Carbonic acid (C O 2 ) = .94 188
2 Carbonate of ammonia 1 ,

(H 2 N 6 CO 2 ) 2 J

96 76 266 12
Forms

1 Protein = . .48 36 14 12

4 Cellulose (C 12 H 10 O 10 ) = 48 40 40

212 Oxygen = . . 212



96 76 266 12

The 212 of oxygen would suffice to convert 53 equivalents of alcohol
into acetic acid.

But if we leave out of the question the nitrogenous substances, the
following scheme will give us the changes that occur in carbonic acid



Online LibraryM. J. (Matthias Jacob) SchleidenPrinciples of scientific botany, or, Botany as an inductive science [microform] → online text (page 10 of 80)