Anton Kerner von Marilaun.

The natural history of plants, their forms, growth, reproduction, and distribution: from the German of Anton Kerner von Marilaun (Volume 1) online

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space, and strongly resembled the striae connected with the cleavage planes of
certain crystals (e.g. of calc-spar). Since these, and generally all cell- walls, light up
the dark field in the polarizing microscope, that is to say, appear doubly refractive,
the assumption was supposed warranted that the cell- walls and other organized
substances consist of crystalline doubly refractive micellae, which lie loosely but
in regular arrangement next one another. It was imagined that every micella was
surrounded, when moist, by an envelope of water, and that on drying, the micellae
came into mutual contact. But later researches have shown that the double
refraction can be produced by pressure and strain in substances which do not
normally exhibit this property, and that the refraction in the polarizing micro-



FORM AND SIZE OF PARTICLES EMPLOYED IN CONSTRUCTION OF PLANTS. 569

scope is not always indicative of the crystalline nature of micellae. The striation
is brought about by dissimilar chemical constitution and unequal quantities of
water in the successive strata of molecular groups, and may be present, equally
well, where the groups of molecules do not possess crystalline form. Moreover,
the results which have been obtained by the so-called carbonization or pulveriza-
tion of the cell-walls goes against the assumption of crystal-like micellae. By
treating with sulphuric acid, heating up to 60-70C., and then operating with
hydrochloric acid, the cell- wall is broken up into extraordinarily small fragments,
exhibiting parallel strise and frequent clefts; and these often subdivided into short,
very fine filaments, which filaments break up by pressure into granules imbedded
in a homogeneous gelatinous matrix. A definite geometrical crystalline form
cannot be demonstrated in this ground-substance. Moreover, the granules are not
bounded by plane surfaces and rectilineal edges, and have no resemblance to the
smallest visible portions of crystals. All the observations obtained by this class
of experiment tend rather to show that the granules are grouped into filaments,
or lamellae, or both, that they are joined together by extremely delicate proto-
plasmic threads, and that the cell-wall possesses a reticular structure. If these
granules and filaments are not themselves the micellae, but groupings, rather, of a
higher order, still their outlines in no case suggest the forms of crystalline micellae.
The idea that the micellae possess a reticular form was corrected much earlier. If
the same rule which prevails in the grouping of the molecules into micellae would
also hold in the association of micellae into groups of high order, and ultimately
into bodies which are in their outline recognizable by our senses, then one might
hope to derive the form of the micellae, and even the form of the molecules
themselves, from the form of the smallest visible portions of the plant. This
supposition would lead to the conception of reticular micellae and reticular mole-
cules in the organized parts of plants. It is, however, very noticeable that all
researches concerning the form of the smallest visible elements of protoplasm point
to a reticular structure. In the dry coating of the so-called plasmodia of myxo-
mycetes, which contains no cellulose, but consists of protoplasm (in which are
deposited crystals of calcium oxalate), for example, in the plasmodium of Leocarpus
fragilis, it is seen that the entire papery skin consists of twisted threads extend-
ing in all directions, which anastomose in a reticular manner, and that the meshes
of this net- work are filled with a highly refringent substance.

In the hyaline ectoplasm of the living protoplasm which inhabit the cell
chamber, very fine threads have been observed lying side by side, and if this
protoplasm is displaced and killed by alcohol, it can be ascertained by the aid of
colouring matters that the whole cell-body is built up of very minute threa,
connected into a net-work, and that the meshes of this fine net-work are filled wit
a fluid substance. Within the threads are to be seen, however, corpuscles arrangec
in rows, which have received the name of microsomata.

The whole protoplasmic cell-body, including the cell-nucleus, appears gen
to possess this same structure, for in the processes which lead up to the divis



570 FORM AND SIZE OF PARTICLES EMPLOYED IN CONSTRUCTION OF PLANTS.

of the cell we always see therein granules, rods, and shorter or longer, straight
and curved tortuous threads, twisted in balls, and anastomosing into net-works,
which undergo the most wonderful displacements, as will be described in the
following pages.

All these observations at any rate do not contradict the supposition of reticular
micellse; and since the conception of molecules built up from atoms grouped in
this manner has not been contradicted by chemists, the hypothesis should find
support from this fact. Of course the hypothesis of the net-like form of the
micellse is based upon an assumption, the accuracy of which is subject to many
doubts. It is questionable whether the same rule always holds in all these
groupings and connections. Just as pointed crystals often join up into spherical
groups, whose construction follows other laws of symmetry than are observed
by the molecules of which the individual crystals are composed, so it is always
possible that the combination of the micellse into visible bodies follows other
rules than the union of the molecules into the micellas.

This change in the relations of symmetry, occuring in minerals, gives rise
to the idea of the possibility that micellse may possess a spherical shape, that
is to say, the highest degree of symmetry which can be imagined in a body.
Some form of symmetry must exist under all conditions, and if the crystalline
form of micellse is excluded, then there remains the possibility of reticular and
spherical micellse.

Although our thirst for knowledge finds but little satisfaction in hypotheses
of this kind, still they are not on this account to be held in contempt. The
minutest structure of every substance, whose movements appear to the perception
of our senses as life, is far too complicated for us to be able to bring it into the
scope of our observations on the life of plants; and in order that we may be
able to form a clear picture of all these matters, it is better at any rate to
imagine the groups of molecules as net- works and spheres than to imagine nothing
at all.

Though we may deny to the micellae a crystalline nature, actual crystals can
be produced by many organized portions of plants. Groups of crystals of calcium
oxalate (see fig. 123 4 ) are found very regularly deposited in the net- work which
forms the pellicle of myxomycetes. Such groups of crystals are also to be found
in the cell-membranes of many flowering plants (Cactacese, Nyctaginese, Com-
melynacese, &c.). The carbonate of lime excreted in the cell-walls of Litho-
thamniese, is likewise crystalline. In other cases these excretions and depositions
of lime and of silica are not crystalline, but amorphous, which literally means
without form. But we must be careful not to be misled by this expression.
These substances cannot be conceived of without a definite shape governed by con-
ditions of symmetry, only they are not composed according to the laws of symmetry
governing crystals, and the word amorphous should therefore be interpreted here
as non-crystalline. It does not lie within the scope of these remarks to enter
into details about the hypotheses as to the shape of the molecules and groups of



FORM AND SIZE OF PARTICLES EMPLOYED IN CONSTRUCTION OF PLANTS. 571

molecules of amorphous lime and amorphous silica; but this much must be said
with regard to these depositions, that they cannot be looked upon as organized
substances.

Here is the proper place to consider investigations as to the size of molecules.
In these researches, especially for the ascertainment of the size of molecules of
gas, very various physical facts offer themselves as data, such as the coefficients
of condensation, the deviations from Boyle's law, the variability of the coefficients
of expansion, the heat of evaporation, and, finally, the constants of dielectrics.
The results differ considerably. For example, the estimates of sizes given for a
certain gas by different methods differ from one another far more than those
which have been obtained from different gases by one and the same method. But
all calculations agree that the diameter of the hypothetically spherical molecules
of gas must lie between the hundred-thousandth and the millionth part of a
millimetre, and that these limits cannot be overstepped, either above or below, to
any great extent even in the extremest cases. A cubic millimetre of gas would
therefore contain about 866 billions of molecules, and if the gas were condensed
into a fluid, the number in a millimetre would increase to a trillion.

The length of light-waves is of the smallest of measurable dimensions. If
the diameter of a molecule is taken in round numbers at the millionth part of a
millimetre, this is 700 times smaller than the wave-length of red light, and the
diameter of a molecule bears about the same proportion to a millimetre, as a
millimetre to a stretch of 2 kilometres. Particles of these dimensions are
beyond the conception of our senses; even the highest powers of the microscope
are unable to disclose them to us, as is shown by the following considerations.
Sheets of gold-leaf are produced, whose thickness amounts to only a hundredth
part of the wave-length of light, and which accordingly contain only 3-5 molecules
of gold above one another. These gold-leaves are transparent to white light,
and this may be regarded as a proof that rays of light penetrate through the
chinks between the molecules. Nevertheless this leaf appears as a continuous
mass under the best microscopes, and it is not possible to recognize the individual
molecules composing it. Under the most favourable circumstances, our microscopes
are able to render visible only particles which comprise perhaps two million
molecules. Since there are no certain data to enable us to measure how great
is the number of molecules from which micellae are built up, and in what manner
the molecules are grouped in them, it would be rash to attempt any conjectures
as to the size of micellse. The possibility of perceiving micellae with the micro-
scope in their outline and shape, especially those of albuminous bodies, whose
molecules are composed of such a large number of atoms (see p. 456) is not to be
wholly excluded, particularly since our microscopes are still capable of much
improvement. Still, the probability is but a remote one, and as matters stand at
present, all conclusions on this subject would be of the nature of theory, in
which one uncertain hypothesis has to furnish the foundation for a second,
still more doubtful.



572 VISIBLE CONSTRUCTIVE ACTIVITY IN PROTOPLASM.



VISIBLE CONSTRUCTIVE ACTIVITY IN PROTOPLASM.

Though it is improbable that we shall ever succeed in seeing the micellae of
which the organized living portions of plants are built up, and though all attempts
to form a picture of these tiny units are only founded upon conjecture and hypo-
thesis, still we can follow with our eyes the general operations, the constructive
and shaping activity of the protoplasm.

This formative activity can be most easily observed in the comparatively large
protoplasmic bodies of myxomycetes, in their so-called plasmodia; therefore some of
the most striking of these processes will now be briefly described.

The myxomycete Leocarpus fragilis, which commonly occurs on the bark of
dry, fallen branches of the Pine, forms a viscous yellow mass, looking deceptively
like the spilt yolk of an egg. The dead branch is covered by a thin layer of this
substance, in which no particular projections can be recognized. Quite late in the
evening Leocarpus can be seen in this plasmodial stage. During the night, how-
ever, it rises up in certain places into knobs and warts, and the whole mass then
has a coarsely granular appearance. Towards morning, pear-shaped bodies, sup-
ported on thin stalks, are produced from these protuberances, which are now no
longer viscous, but exhibit a thin dry pellicle. Within, they have become trans-
formed into numerous hair-like threads, with black powdery spores lying between
the threads. Leocarpus needs about 12 hours for this manifestation, and if one has
the patience to observe the mass shaping itself throughout the night, one may
actually see how it rises from the substratum, rounds itself off, forms a skin, and
assumes the pear-shape form. Dictydium umbilicatum develops its plasmodia in
the same way as Leocarpus. The light brown, irregular, flowing mass of proto-
plasm gathers itself up into a round cord, which becomes thickened in a club-
shaped manner at its upper end, and then spreads out into a delicate net -work
with spherical outline. Between the meshes of this net-work the protoplasm
separates out into black powdery spores, which are at the mercy of the slightest
breath of wind. The slimy protoplasm of Stemonitis fusca, on the other hand,
rises up in the shape of numerous closely-compacted strands about 1J cm. long.
Each individual strand is divided into a lower, stalk-like portion, and an upper,
thick, cylindrical body. This is at first of slimy consistency, but soon becomes dry
and divides into a central axis, from which proceed all round an endless number of
very fine reticulating threads which break up into thousands of powdery spores,
and at the periphery into a very delicate skin, which later on ruptures and allows
the spores to fall out. This entire shaping of the protoplasm, with which is con-
nected a change of colour from white to purple, is accomplished under the eye of
the observer in about ten hours. The protoplasm of Chondrioderma difforme can
scarcely be distinguished from that of Stemonitis fusca, and yet how very different
is the form which it assumes as a plasmodium. First, it is massed into a round
ball, and in this is separated out an enveloping skin of innumerable single slender



VISIBLE CONSTRUCTIVE ACTIVITY IN PROTOPLASM. 573

threads, and a large quantity of dark spores which fill up the space inclosed by the
skin. Soon after, the skin breaks up into stellate projecting lobes at the free apex
of the spherical body, and now the dark spores can pour out of the open vesicle.

The protoplasm of Didymium shapes itself quite differently, and that of
Clatroptychium differently again. If we were to exhaust the multiplicity of form
which the protoplasm of this group of plants assumes, we should be obliged here
to actually describe the shapes of all myxomycetes. The above examples will
suffice for the establishment of the fact that apparently quite similar protoplasm
becomes, in each species, speedily transformed into a definite structure. It only
remains to be noticed that the shape assumed by the specifically different proto-
plasm is quite independent of external conditions ; and that in the same light, with
the same degree of humidity, and at the same temperature, under the same glass
shade, the pear-shaped Leocarpus, and the cylindrical strands of Stemonitis develop
side by side (for illustrations of Myxomycetes cf. vol. II., fig. 355).

The pellicle which bounds the plasmodia of myxomycetes contains no deposited
cellulose, and there is consequently in these plants generally no distinction
between the pellicle and the body of the cell. The protoplasm of other plants,
however, always provides itself, sooner or later, with an envelope in which cellulose
can be demonstrated. Of course, cellulose is often present in the cell-wall only in
small amount ; thus, in yeast, as well as in the majority of fungi, the main part of
the membrane is formed of nitrogenous compounds. Various phenomena lead to
the conclusion that by the development of cellulose in the skin, advantages are
obtained which are not enjoyed by myxomycetes, with their brittle pellicle built up
of firm nitrogenous compounds. The soft protoplasm is better protected against
injurious external influences by the cellulose wall, and the whole structure obtains
that firmness and strength which are absolutely necessary, especially to plants
composed of numerous cells.

Moreover, the cell- wall must not be conceived as always a rigid covering,
as a chamber with immovable walls. In many instances it is rather to be
compared to the skin of an animal, which adapts itself to each alteration in
the shape of the body. In no case is the elasticity of the protoplasm hindered
by the surrounding cell-wall. Frequently the cell-wall takes no share in the
visible plastic processes of the protoplasm which it incloses, and it usually perishes
when the transformations have been completed in the space it surrounds and
protects. In many instances, on the other hand, the outline and shape of the cell-
wall alter in correspondence with the alteration of the protoplasm inclosed by it.

These remarks had first to be made in order to rightly understand the plastic
processes to be described successively as Segregation, Gemmation, and Cell Division.

In the case of the Segregation associated with most of the previously described
plasmodia, it is to be pointed out as characteristic that the protoplasm divides
within a rigid, enveloping cell- wall into completely separate portions of identical
shape, and develops no partitions continuous with the surrounding cell -wall.
The inclosing cell-wall stands in no direct contact with the formed protoplasmic



574 VISIBLE CONSTRUCTIVE ACTIVITY IN PROTOPLASM.

masses. Even when the wall remains, and is not ruptured nor disintegrated, it is
separated from the protoplasmic masses by the new cell-walls, with which these
have meanwhile surrounded themselves. For every species of plant the number,
size, and shape of the bodies arising in the interior of a cell by division are
quite definite, though they vary from species to species. In the cell-chambers
of some species several thousand minute protoplasmic bodies arise. In others,
again, the number is very limited. Frequently, indeed, the protoplasm only splits
up into two similar halves. If the number is large, the individual masses are
exceedingly small, and can only be recognized when very greatly magnified. If
the number is limited, the divided portions are comparatively large. The shape
of the structures is exceedingly various. Some are spherical, elliptical, or pear-
shaped; others elongated, fusiform, filamentous, or spatulate; some are straight,
others are spirally twisted, and many are drawn out into a thread; others are
provided over the whole surface with short cilia, others again with a crown of
cilia at a particular spot, or with only a single pair of long cilia. The illustration
on p. 29 represents the most widely differing forms, without, however, exhausting
the wealth of configuration. In the majority of cases the small bodies exhibit
active movements, and that even within the cell-covering which surrounds the
dividing protoplasm ; but sooner or later they come to rest, and then assume another
shape, or fuse with another protoplasmic body.

With regard to the further changes experienced by the bodies formed by
division, many events may be distinguished. In one, the cell in which the division
of the protoplasm has taken place opens, the bodies formed glide out separately
and swarm in the surrounding fluid. Often they are concerned in fertilization, and
fuse with other protoplasmic bodies in a manner to be described later in detail. If
not, they surround themselves with a cell-wall, but do not adhere together, or
develop into a cell-colony.

In the Water-net (Hydrodictyori), described on p. 36 (cf. fig. 197, vol. II.), the
parietal protoplasm of a cell divides up into 7000-20,000 minute clumps which
exhibit the so-called swarming movement. At first a definite aim cannot be
assigned to these movements, but after a short time the particles appear arranged
very regularly in a net with hexagonal meshes. They assume the form of short
rods, each of which joins at its poles with two others, being cemented to them
by excreted cellulose. Instead of a protoplasmic parietal layer in the cell in
question a miniature water-net is now seen to have arisen. This becomes free
with the disintegration of the parent-cell; its cells grow and increase in all
directions without, however, altering the shape once assumed. The process which
is observed in Pediastrum (fig. 197, vol. II.), a very small water plant allied to the
water-net, is very much the same. Here also the protoplasm of a cell which has
isolated itself from the others divides up into small clumps which round themselves
off, and swarm about for a short time. Gradually they come to rest, assume an
angular form, and arrange themselves so as to form two concentric rings in one
plane. Where they come into contact with each other, they excrete cellulose and



VISIBLE CONSTRUCTIVE ACTIVITY IN PROTOPLASM. 575

thus become connected into a tiny disc. This disc consists of as many cells as there
are connected clumps of protoplasm, and presents almost the appearance of a honey-
comb. Out of this combination each cell can again separate itself from its com-
panions, its protoplasm can divide up afresh, and generally the whole process
described above may be repeated.

The Water-net and the discs of Pediastrum develop young nets and discs
accordingly, from the divided protoplasm in the individual cells. These escape as
small colonies of cells from the space in which they were formed, and here a
definite isolation of the young cell-colony occurs. In Glceocapsa, on the contrary,
of which a species (Glceocapsa sanguinea) is represented in figure 25A, n and o,
the young cell-groups remain joined together. Each cell always divides up, two
and two, into protoplasmic clumps, which surround themselves immediately with a
thick cell-wall. The old cell-wall, however, does not disintegrate nor rupture ; it
does not allow the young cell-colony to escape, but it stretches, and the young and
old cell-walls are now seen layered one above another. If this process is repeated
many times, protoplasmic balls arranged in pairs are to be seen inserted within a
whole system of concentrically stratified cell-walls. A process similar to that just
described is observed in the ovules of seed-plants, and has been called, though not
very happily, "free cell-formation".

Gemmation is essentially different from the process just described. It is
observed in plants both with and without chlorophyll, but is not really frequent
in the vegetable kingdom. Its characteristic feature is that the protoplasm at a
certain point of the circumference of a cell pushes outwards, and in this way a wart
or bud-like elevation of the cell-wall, an actual protuberance, arises which, though
at first not very prominent, soon increases in area, and in the end assumes the size
and shape of the body from which it was produced. We may distinguish two
kinds of gemmation. Either an open communication is maintained between the
outgrowth and the structure from which it was produced, and no separation occurs
at the place of origin ; or, the parent cell is shut off from the outgrowth by a cell-
wall which subsequently splits, and the outgrowth is detached from the cell-body
from which it arose. Very pretty examples of the first kind are exhibited by the
Siphoneae, especially in Vawcheria, illustrated in figure 25A, a. The tubular cells
appear branched, each branch consisting of a tube ending blindly, and all these
branched tubes are in free communication with one another. The entire Vaucheria
is really only a single, much-branched cell of course a cell which must be called
gigantic in comparison with ordinary plant-cells. Species of the genus Bryopsis
shape themselves similarly, but in these the outgrowths are much more regular
than in Vaucheria, the whole cell, branched and thus pouched, almost resem-
bling a moss with axes, leaves, and rhizoids. In the genus Caulerpa the cell
also produces outgrowths, some of which resemble roots, whilst others imitate the
shapes of leaves, reminding one, in some species, of small fern-fronds.

Of the second kind of gemmation yeast may be taken as a type. The shape
of individual yeast-cells is ellipsoidal. When the yeast-cell grows, the elliptical



576 VISIBLE CONSTRUCTIVE ACTIVITY IN PROTOPLASM.

form of the body is retained for a time, and the ellipsoid increases equally on all
sides. When it has once attained a certain size, the protoplasm bulges out at a



Online LibraryAnton Kerner von MarilaunThe natural history of plants, their forms, growth, reproduction, and distribution: from the German of Anton Kerner von Marilaun (Volume 1) → online text (page 70 of 93)