Principles of the anatomy and physiology of the vegetable cell

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PHYSIOLOGY OF THE Vig@gE TABLE CELL.

PRINCIPLES

OF THE

ANATOMY AND PHYSIOLOGY

OF

THE VEGETABLE CELL.

BY

HUGO VON MOHL,

DOCTOR OF PHILOSOPHY, MEDICINE, AND SURGERY;
KNIGHT OF THE ORDER OF THE WURTEMBURGH CROWN; ORDINARY PROFESSOR OF
BOTANY IN THE UNIVERSITY oF TUBINGEN 3
MEMBER OF THE DUTCH INSTITUTE; OF THE ACADEMY OF SCTENCKS
OF STOCKHOLM ;
MEMBER OF THE IMPERIAL LEOPOLD-CAROT. ACADEMY OF NATURALISTS ;
CORRESPONDING MEMBER OF THE INSTITUTE OF FRANCE: OF THE ACADEMIES OF
SCIENCES OF BERLIN, MUNICH, TURIN, AND VIENNA.

CORRESPONDING

TRANSLATED

(With the Author’s permission)

BY
ARTHUR HENFREY, F.RS, F.LS, ETC.,

Lecturer on Botany at St. George's Hospital ; Author of Outlines of Anatomical and
Physiological Botany ; Rudiments of Botany ; ete., ete.

GAith an MMlustratibe Wate and mumeraus GA noveuts,

O32) ON:
JOHN VAN VOORST, PATERNOSTER ROW.

MDCCCLII.

LONDON
T. E. Mercarr, Printer, 68, Sxow Hitt.

AUTHOR’S PREFACE

TO THE

ENGLISH TRANSLATION.

Mr. Arraur Henrrey having informed me that he
intends publishing an English translation of the pre-
sent treatise, I take this opportunity of making known
to the English reader the purpose I had in view in the
preparation of the book. The following pages were not
originally intended to appear as an independent work,
or to give a summary of the wide subject of the
Anatomy and Physiology of Plants, but appeared as
an article, in the “Cyclopedia of Physiology” published
by Dr. Rudolph Wagner, of Gottingen, drawn up to
furnish students of Animal Physiology, and more
particularly the Medical Profession, with a review of
the Anatomical and Physiological conditions of Vege-
tables (of the Cell), in order to enable them to form
a definite judgment upon the analogies which might be °
drawn between the structure and vital functions of
animals and plants. This intention, together with the
circumstance, that I was compelled to crowd the whole
exposition into the space of a few sheets, rendered it
necessary to direct especial attention to the individual
cell, as the fundamental organ of the Vegetable Orga-
nism. Since, however, the cell only presents. itself in
anatomical and physiological independence in the lowest

Iv PREFACE.

plants, and since, in the more highly organized plants,
both the structure and the physiological functions of
the individual cells become subject to greater depend-
ence upon the other parts of the plant, in proportion
as the collective organization of the vegetable is more
complex ; moreover, since functions then present them-
selves, of which no trace can be found in the lower
plants, it became requisite to take account of the plants
of higher rank, and of the various organs which these
possess. The treatise, therefore, contains, if an imper-
fect, still in many respects, a more éxtensive resumé of
Vegetable Physiology, than might be conjectured from
the title.

Unhappily, the Physiology of Plants is a science
which yet lies in its earliest infancy. Few of its dog-
mas can be regarded as settled beyond doubt; at every
Step we meet with imperfect. observations, and con-
sequently with the most contradictory views; thus,
for example, opinions are still quite divided regarding
the doctrines of the development of the cell, of the
origin of the embryo, and of the existence of an im-
pregnation in the higher Cryptogams. Both in these
and in other cases, the small compass of the present
treatise forbids a more extensive detail of the researches
upon which the opposing views are founded; I hope,
however, that I have succeeded in making clearly pro-
minent, the chief points upon which these contests turn,
and thus, in facilitating the formation of a judgment
by the reader ; and, I have never neglected to indicate
the literature from which further instruction is to be
derived.

HUGO VON MOHTL.

Tupincen, October 19th, 1851.

CONTENTS.

Introductory Remarks ,
I.—The Anatomical Condition of Ge Cell
A. Form of Cells
B. Size of the Cell
C. The Cell-membrane _
a. Physical Properties
6. Structure
c. Chemical Cnn
. Cells in their Reciprocal connexion
. Contents of Cells
a. Primordial Utricle, Protoplasm, and Nucleus
6. Cell-sap , ;
ce. Granular cane :
d. Compounds dissolved in the Cellsap
‘, Origin of the Cell :
a. Division of the Gall
b. Free Cell-formation
1i.—The Physiological Conditions of the Cell
A. The Cell as an Organ of Nutrition
a Absorption of Watery fluids
6. Diffusion of the Sap in the Plant
c. Nutrient Matters . ;
d, Elaboration of the N alee
e. Secretions j
J. Evolution of Heat
B. The Cell as an Organ of Propagation
- The Multiplication of Plants by Division
Propagation by Spores and Seeds
i. Propagation by Spores .
Propagation of Thallophytes
“* Propagation of the Cryptogams \
having Stems and Leave
6. Propagation by Seeds
* The Pollen
** The Ovule 7
*,* The Origin of the Embryo
The Cell as an Organ of Motion.

EXPLANATION OF THE PLATE.

Fics. 1—6. Conferva glomerata.

1. The growing points of the plant.—a, Terminal cell; b. Rami-
fication of a cell, beginning ; c, Ramification further advanced,
with the commencement of the formation of a septum at its
base ; d,a perfect septum ; e, Prolongation of a branch-cell
twice the length of the cells in general, with the commence-
ment of the formation of a septum in the middle.

2. Terminal cell grown to the double length, with an imperfect
septum in the middle.

. Constriction of the cell-contents by the half-completed sep-
tum.

. A half-completed septum, in which a considerable deposition of
cellulose membrane has already taken place.

. A septum in progress of formation after the action of an acid,
which has caused contraction both of the primordial utricle
(a) and the cell-contents (6).

. Complete septum split into two lamelle by the action of an
acid.

. The two uppermost cells of a hair from the filament of Vrades-
cantia Sellowii, with nuclei and currents of protoplasm.

Fies. 8—11. Formation of the Pollen in Altheea rosea.

8. Four nuclei in the contents of the parent-cell, with the com-
mencement of the formation of four septa. The primordial
utricle and cell-contents contracted from the action of alcohol.

9. Farther advanced development of the septa of the parent-cell.

10. The primordial utricle removed from the parent-cell, not yet

completely divided into four parts.
11. Completed division of the parent-cell.

Gi pt ine eA ALAM Stra ORUN Aa ere eg BEC sins wele hdiepaenreeny
en wa eg ee ae a Te

EXPLANATION OF THE PLATE.

Fires, 12—18. Formation of the embryo in Orchis Morio

(from Hofmeister).

. 12. The ovule, a considerable time before fertilization. a, the outer

coat ; 6, the inner coat ; s, the embryo-sac ; ¢, the funiculus.
Three nuclei have been formed in the micropyle end of the
embryo-sac.

18. The internal parts of the ovule a short time before fertilization.
a, inner coat of the ovule ; s, embryo-sac ; }, germinal vesicle.

14. The ovule at the moment of fertilization, a, b, s,as in the pre-
ceding figure ; p, the pollen-tube ; f£ a few cells which have
made their appearance at the chalazal end of the embryo-sac.

15. Further development of the impregnated germinal vesicle. It
contains two nuclei which lead to its division into two cells.

16. The embryo-sac with a pollen-tube adherent. The germinal
vesicle is parted into two by division into an upper (a) and
a lower (0) cell.

17. The pro-embryo (Vorkeim). Its superior portion (a), the sus-
pensor, has originated through the division of the cell a of
Fig. 16 ; its inferior portion, the rudiment of the embryo (6)
through the division of the cell 6 of Fig. 16.

18. An embryo (6), with its suspeusor (a), in a farther advanced

stage of development.

Fies. 19—22. Spores of Prolifera rivularis (from Thuret).

19. Moving spore possessing a circle of ciliz.
20—22. Various stages of the germination.
23. Two ciliated spores of Conferva glomerata (from Thuret).
24, Germination of the same (from Thuret).
25, Seminal filaments (Samenfaden, spermatozoids) of Chara (from
‘Thuret).
. Two cells from the antheridium of Sphagnum, with seminal fila-
ments (from Unger).
. An isolated seminal filament (from Unger).
. A seminal filament with two cilie treated with iodine.

9. Seminal filament of Pteris serrulata (from Leszcye-Suminski).

ANATOMY AND PHYSIOLOGY

OF THE

VEGETABLE CELL.

INTRODUCTORY REMARKS.

Ir we examine the texture of plants with a powerful microscope,
we find that it does not consist, as appears to the naked eye or
under slight magnifying power, of a homogeneous substance per-
forated by a greater or less abundance of cavities, but is composed
of minute portions, of definite form and organization, separable
from each other (the elementary organs).

Observ. Universal as the agreement among phytotomists has been for
some thirty or forty years on this fundamental proposition of vegetable
anatomy, it was a long time before it acquired general recognition.
The very founders of the anatomy of plants, Leeuwenhoek, Malpighi, and
Grew, were, indeed, led by their researches to the detection and distinc-
tion of the elementary organs as organized parts, but the real conditions
were again misconceived throughout the whole of the eighteenth century.
On the one hand, Ludwig and Bohmer, seeking an analogy with animal
cellular tissue, described vegetable cellular tissue as a mass of irregular
fibres and lamelle interwoven together ; on the other hand, C. F. Wolff
(theoria generationis) described vegetable substance as a homogeneous
mass hollowed into holes and canals, a view which still found an active
defender during the first ten years of the present century, in Brisseau de
Mirbel, and is even now held by him to be the condition in the earliest
stage of development of vegetable tissue, if not that of the subsequent
stages. More correct views were first substantiated by German phytoto-
mists of the present century.

The primary form of the elementary organ of plants is that of
a completely closed, globular, or elongated vesicle, composed of a
solid membrane, and containing a fluid (utricle, utriculus). If
this remains still closed after its development is completed, it is
called a cell, cellula ; but if a row of utricles arranged in a line
become combined, during the course of their development, into a
tube with an uninterrupted cavity, through the absorption of their
cross walls, a compound elementary organ is produced,—the vessel
(spiroid of Link).

Observ. The tracing back of the whole of the elementary organs to
the primary form of the utricle, has been accomplished only quite recently.
The earlier phytotomists, who took the elongated cells for long tubes,
overlooked their analogy with the short cells, believing that they were
rather to be compared with the vessels, and they described them as a
Special anatomical system under different denominations (fibres, lympha-
tic vessels, &c.), in which error they were followed even by Treviranus

B

te seats re woe ats

bs ANATOMY AND PHYSIOLOGY OF

(“ Physiolog.” i. 64), although Sprengel, Rudolphi, Link, and Kieser had
already recognized that they all were modifications of the cell. Far less
than this was the true nature of the vessels perceived by the earlier phy-
totomists ; and I believe that I was the first to detect their origin from
rows of closed cells (“Memoirs of the Acad. of Munich, i. 445. De struc-
tura palmarum, § 26—29). No sharply defined line can be drawn be-
tween vessels and cells, for reasons which will be hereafter discussed.
Whether the milk-vessels, which indeed occur only in a comparatively
small portion of plants, and play a very subordinate part both in ana-
tomical and physiological relations, originate in an analogous manner from
rows of cells, or are to be regarded as a system essentially different from
the rest of the elementary organs, is a question upon which no opinion
has yet acquired an universal acceptance. Unger asserts the former
(“Annals of the Vienna Museum,” ii. 11) ; but it is more than doubtful
whether his observations were accurate, and it seems that the milk-vessels
ought to be regarded as membranous linings of passages which appear be-
tween the cells. (See an anonymous memoir in the “Botanische Zeitung,”
1846, 833, entitled “The Milk-vessels : their Origin, &e.”)

The basis of the substance of all vegetables consists of the
cells, since even in the most highly developed plants all the
organs are in the youngest condition composed of cells alone, and
the vessels only appear during the subsequent development. In
the lower plants (Fungi, Algze, Lichens, Liver-mosses and Mosses)
all the elementary organs persist in the organization of the cell.

Observ. The circumstances, that a plant is composed of cells alone, or
also possesses vessels, have not that importance either in a systematic or a
physiological point of view which De Candolle attributed to them, when he
used them for the primary division of the vegetable kingdom, into Cellular
and Vascular plants, for these conditions do not run parallel with the total
organization of plants, since there exist both Cryptogamic and Phanero-
gamic plants with and without vessels,

I. THE ANATOMICAL CONDITION OF THE CELL,
A. FORM OF CELLS,

The forms under which cells present themselves are so manifold,
that a special examination of all would occupy a far greater space
than can be devoted to it in this place ; I therefore confine my-
self to a few observations,

In the first place, in examining the form of the cell, we have to
take notice that it depends upon two circumstances. On one hand
the form of the cells is determined, like that of every organic
body, by its indwelling laws of development; on the other hand
the individual cell, in the far greater majority of cases, cannot
follow those laws uninterruptedly, because it forms part of a com-
pound tissue, and is compelled by its intimate connexion with the
surrounding elementary organs, to accommodate itself to the space
thus determined for it, and in consequence of the pressure to
which it is exposed laterally from the surrounding elementary

ne a ne ee ee

THE VEGETABLE CELL. 3

organs, to assume forms which would be foreign to it under con-
ditions of free, unrestrained development.
The sphere must be regarded as the fundamental form, in which
every freely developed cell first appears. Although this form oc-
curs not unfrequently with great regularity in very young cells,
this is more rarely the case in full-grown cells. For in most in-
stances the growth of cells is by no means uniform ; sometimes one
diameter remains short and the cell assumes the form of a flattened
ellipsoid ; but far more often one of the diameters becomes more
or less elongated, and the cell passes into the form of an elon-
gated ellipsoid, or, by farther extension, into that of a cylinder.
Roundish forms are found more or less regularly developed in many
lower Algze, e.g., in Protococcus, in the yeast plant, in completely
or almost wholly isolated cells of higher plants, as in spores and
pollen-grains, in the knob-shaped ends of many hairs of plants, &c.
The cylindrical or attenuated conical forms are likewise frequent in
the lower orders of the vegetable kingdom, in hairs, and the like.
The frequently occurring form of the elongated ellipsoid, and
still more the cylindrical shape, point to the innate tendency of
the vegetable cell towards an unequal growth, in which an oppo-
sition manifests itself between the longitudinal axis and the
transverse axes, between the upper and lower ends, and the
lateral faces of the cell; but in many other cases a still greater
deviation from the primary form is met with, where particu-
lar points exhibit an isolated growth, giving rise to papillary
elevations and gradual development of these into cylindrical pro-
cesses, and thus to a ramification of the cell. The
phenomenon is very common ; it occurs, for instance, Fig. 1.
in the formation of the pollen-tubes upon the stigma,
in the germination of most spores, and in the most
Striking degree in many Alge. In these last the
ramifications produced at the lower end of the cell
frequently form a contrast to the upper end, since
they fulfil the functions of root fibrils, e. g., in Botry-
dium (fig. 1),in germinating Conferve, &c., while the
protrusions sprouting out from the upper end form
the foundation of abundant, often very regular, rami-
fications of the plant, ¢e.g., in Vaucheria, Bryopsis,
&e. This phenomenon is seen most distinctly m uni-
cellular Algze, as in the genera just named; but in
most cases this process of ramification is combined
with cell-division, which renders the detection of it
difficult, and the uni-cellular becomes converted into a cate FF
F es: 2 : 4 Botrydium granu-
es plant, e.g.,in Conferva glomerata (pl. A, “iatuia.
gs. 1—6).
este cells which have grown together with other cells or with
vascular utricles, into a tissue, exhibit much slighter differences
of form than the freely developed cells. It is true that in this
B 2

4

ANATOMY AND PHYSIOLOGY OF

case even a greater complication of form may arise from the

growing out of particular places through unequal development,

when one side of a cell lies free upon the external surface of a
ry plant or in one of its internal air-
Mg. 2.

cavities, as is evident in many hair-
structures, and in the star-shaped
cells of the air-cavities of the Vym-
phoce (fig.2); but in most cases such
irregular growth of individual cells
is rendered impossible, simply by
the mechanical conditions in which
they are placed. It is a general
rule, that cells combined into a tis-
sue are bounded by a number of
plane surfaces, instead of possess-
ing a rounded external form, since

that part of a cell by which it is adherent to another cell becomes
flattened, and only the free parts of the cell-wall can follow the

Fig. 3.

Liber-cell of
Cocos botryophora.

original tendency to become rounded. The form of
such cells depends, therefore, principally upon their
relative position, and their more or less crowded
condition ; and the further modification of the form
depends upon whether the dimensions of the cell in
different directions are pretty nearly equal, or one
dimension considerably exceeds the rest.

Taking into consideration, in the first place, the
latter condition, we can divide cells combined into
a tissue, by no means, however, very strictly, into
the short and the elongated.

The short cells, developed pretty uniformly in all
directions, form the elements of the structure of all
higher plants, since all their organs are formed, in
their earliest stages, of these alone, and even in full-
grown plants the bark and pith of the stem,as well
as the soft parts of the leaves and the organs of
fructification in general, are composed of cells of
this form. During the development of the indivi-
dual organs, fibrous strings are formed in the
cellular mass constituting their ground-work, and
these fibrous strings, which are composed of elon-
gated cells and usually also of vessels, which lie
among the elongated cells, receive in this case the
name of vascular bundles, and taken collectively
constitute the wood of the plant. The mass com-
posed of short cells, in which the vascular bundles
are imbedded, is named, in contradistinction to the
latter, the parenchyma.

The elongated cells of the vascular bundles

- THE VEGETABLE CELL. 5

(fig. 3) are, as a rule, distinguished from the short parenchymatous
cells, not only by their elongated, often fibrous shape, but also by
the two ends being attenuated to points. In this case they are not
arranged end to end in lines, but their attenuated extremities are
interposed between the lateral surfaces of the cells situated above
and below them; while the parenchyma cells, if, as is usual, they
are arranged in lines, stand one upon another with flattened ends,
their cavities being thus separated by partitions directed at right
angles to their longitudinal axes. Link founded upon this difter-
ence of the ends the distinction between parenchymatous and pro-
senchymatous cells, a distinction which is indeed well grounded
when we compare extreme forms, but which is by no means to be
carried through, since the most manifold transitions occur from
parenchymatous cells, with more or less oblique cross-walls, to
perfect prosenchymatous cells.

_In many Thallophytes, especially in many Fungi (e. g., Boletus
ignierius) and Lichens (¢. g., in Evernia), isolated portions of
the substance are found of fibre-shaped, frequently irregularly
interwoven cells (irregular cellular tissue of Kieser). Gradual
transitions also occur from this form of cell to the form of the
parenchymatous cell.

The form of the parenchymatous cells is most intimately con-
nected with their relative position.

The simplest condition is afforded by such cells as lie one above
another in a simple row, as the cells of the Conferve (pl. 1, fig. 1),
articulated hairs, &c. Here the cells become flattened on the sur-
faces of contact, while the side-walls retain their natural curvature.
Accordingly as these possess a cylindrical curvature, or one more
approximating to a globe, does the entire cellular filament obtain
a cylindrical or beaded shape.

When parenchymatous cells lie side by side in a
simple layer, as is the case in the leaves of most Mosses
and Jungermannice, and in the epidermis of the higher
plants, their lateral surfaces, by which they are cohe-
rent together, become flattened; while the lower and
upper free sides are either more or less convex, coni-
cally elongated (fig. 4), or quite flattened like the rest. Cells of the
Taken as a whole, such cells exhibit the form of many- a ee aie
angled plates or prisms, the shapes of which again pre- ?é™ihus bar-
sent modifications, accordingly as the growth of the
cells in the direction of the surface, which they combine to form,
is uniform or irregular. The lateral faces of tabular cells are
usually perfectly flat. Yet it sometimes happens, for instance in
the anthers of Chura, and in the epidermal cells of many leaves
(fig. 5), that the side-walls are curved into waving lines, or zig-
zagged in sharp angles.

It is not so easy to define the form of the parenchymatous cells
when they are collected together in masses (fig. 6), as is the rule

Fig. 4.

AF SPEYER TS ESET T WMS, yEaER eer WY goeinpee 4 ENVELOPES SMITE oN oa a mn, Deere Gages er. oo \ ee Oe

[gee

}

6 ANATOMY AND PHYSIOLOGY OF

in the internal substance of organs, for instance in pith, in bark,
&e., for here every cell ig surrounded on all sides by other cells,
and exhibits as many flattened surfaces ag there are cells standing
in connexion with it. Kieser (“Grundz. der Anatomie der Phlan-
zen,’ § 127) sought to demonstrate, that the form of the cell must
necessarily be that of a rhombic dodecahedron under such circum-
stances, since this form encloses the greatest space within the
smallest amount of limits, and that their form is usually that of a
thombric dodecahedron elongated in a perpendicular direction, be-
cause the primary form of the vegetable cell is not the sphere but
the ellipsoid. This proposition may be admitted theoretically, but
it would be a vain labour to seek actually to observe the form of
the rhombic dodecahedron in a eell in nature, since the contigu-
ous cells are always far too unequal in size for them to become

Fig. 5. Fig. 6.

Epicermis of the Lang face of the leaf of Parenchymatous cells from the bark of
B Helieborus foctidus. . Huphorbia canuriensis.

moulded into regular mathematical forms by their reciprocal pres-
sure. So that in cross sections of a parenchymatous tissue the cells
are found certainly of many-angled but of irregular forms ; and
the faces of transverse slices of the individual cells have a very vari-
able number of sides (usually from five to eight). It is therefore
more suitable to call such cells polyhedral instead of dodecahedral,

On the more or less crowded arrangement of the cells it depends
whether the plane surfaces of these meet at acute angles (fig. 7) ;
or whether, when the cells are more loosely aggregated, the sur-
faces of contact are but small (fig. 6), and large portions of the
cell-walls between them remain unconnected with the neighbour-
ing cells. In the latter case, the free portions of the cells retain
their natural rounded form. In particular cases, however, the
portion of the cell-wall immediately surrounding a plane surface
in contact with another cell, grows out in a tubular form, so that

THE VEGETABLE CELL. v4

when several such processes are formed, the cell acquires a star-like
appearance. When in such cases the cells are arranged in one
plane, as occurs in the cross-walls of the air-canals of many water-
plants, all the rays of the star he in one plane (figs. 8, 9); when, on
the other hand, the cells are heaped together in masses, as in the
pith of Juncus effusus, the rays project from all sides of the cell.

Fig. 7.

Stellate cellular tissue from the leaf-stalk
of Musa.

Cells of the pith of Partition bounding an air-canal in the
Acanthus mollis. leaf-stalk of Sagittaria sagittifolia.

Fig. 10.
Far more frequent than such re- '
gularly branched cells, are those
of a roundish form, exhibiting a
shorter projection at one or more
points, and so having a moder-
ately irregular form ; the paren-

_chyma of the lower side of the
leaves of most plants is com-
posed of such cells (fig. 10).

Observ.- Some phytotomists have eee made ihe
distinguished a greater number of
tissues according to the forms of the cells, applying particular names to

8 ANATOMY AND PHYSIOLOGY OF

them, especially Hayne (“ Flora” 1827, ii. 601), Meyen (“ Phytotomie” 57 ?
“ Physiologie” i, 12), and Morren (“ Bulletin de? Acad de Bruaelles,” V. No. 3).
The arrangement of Hayne, which did not attract the least notice, I may
pass over here. Meyen distinguished: 1, Merenchyma—tissue composed
of spherical cells, the cells only partially in contact ; 2, Parenchyma ; 3,
Prosenchyma—this name was applied by Meyen to the woody tissue of the
Conifers ; 4, Plewrenchyma, which was the name by which he distin-
guished the prosenchyma of all other plants. The division of merenchyma
from parenchyma was superfluous, and cannot be carried out, because there
are so many transitional forms ; the alteration of the established term
prosenchyma into pleurenchyma was altogether inconvenient, and was not
adopted. But the wilderness of botanical terminology would have been
increased beyond all reasonable measure by Morren, had not his subdivi-
sions been passed over unregarded ; for he divided the parenchyma alone
into no less than eight tissues, which he named, merenchyma, conenchym«a,
ovenchyma, atractenchyma, cylindrenchyma, colpenchyma, cladenchyma,
and prismenchyma. All such far-fetched subdivisions of the cellular
tissue are wholly valueless, because no exact connexion exists between
form and function, and frequently enough the same organ is formed of
cells differing considerably in form,—in two closely allied plants.

B. SIZE OF THE CELL.

Important as the accurate determination of the size of the indi-
vidual elementary organ is, in many special researches, particularly
those relating to the history of development, yet in general the
knowledge of the size of cells is of very subordinate value; and
this the more that not only do the cells of the same organ exhibit
extraordinarily great variations in respect to their size, but the
contiguous cells of one and the same organ not unfrequently differ
considerably from each other. Pollen grains afford a very striking
example of the former; their dimensions are tolerably constant in
each species of plant ; but their diameter varies from 1-300th of a
line in Myosotis to 1-15th of a line and more in Cucurbita, Stre-
itzia, &c. The cells of a single organ often differ to the extent of
some being twice or thrice as large as others.

The diameter of the cells of parenchyma may be stated at a
general average of from 1-20th to 1-100th of a line; but in parti-
cular cases (¢. g., in the spores of many Fungi, in the yeast cells) it
falls to less than 1-500th, and in other instances it rises, é@. g.,
succulent parts, in the pith of the elder, &c., to 1-10th of a line and
more ; so that in such cases the individual cells are actually visible
to the naked eye, which is not generally the case.

The dimensions of many elongated cells form a striking contrast
with this small magnitude of the majority of parenchymatous cells,
since while the transverse diameter of the former is usually consi-
derably smaller than the diameter of the parenchymatous cells,
the longitudinal extension is very remarkable. In regard to the
majority of elongated cells, especially the prosenchymatous cells of
the wood and bast or liber of most plants, we should be very much

THE VEGETABLE CELL. 9

_ deceived if we deduced from the fibrous structure of these organs
a great length of the constituent cells; yet, on the other hand,
cases do occur when particular cells exhibit an astonishing length.
The prosenchymatous cells of wood generally exhibit only a length
of 1-3rd to one line, exceeding this last dimension but seldom;
as a rule, the bast cells attain about the same length; yet in some
cases they occur of far more considerable length, for I found them
16 to 2°6 lines long in a Palm (a species of Astrocarywm).
The bast cells of flax and hemp are considerably longer, but diffi-
cult to measure, since it is often impossible to ascertain the com-
mencement and termination of a cell. Many hairs formed of
simple cells also exhibit a very considerable length, especially
cotton, the longest fibres of which do not, however, exceed one to
two inches. Among the cells of the higher plants the pollen grains
are the most striking for their great longitudinal growth, the fili-
form prolongation penetrating into the style attaining in long-
styled plants like Mirabilis longiflora, Cactus grandiflorus, &e., a
length of three inches and more.

The most striking examples of large cells are found in the
family of the Algze, in many uni-cellular plants, as in Vaucheria,
Bryopsis, and especially in Chara, in the larger species of which
the great cells forming the interior of the stem attain the length
of several inches, and a diameter of 1-3rd of a line and more,

Cc. THE CELL-MEMBRANE.
a. Physical Properties.

In most cases the membrane of cells possess a considerable de-
gree of stiffness and solidity. But in this respect extreme dif-
ferences occur between the cells of different plants and of their
different organs; and, moreover, this condition may exhibit ex-
treme variations at different periods of the growth of the same
cell. The membrane of young cells, also the cells of many lower
plants, for example of most Algee, Fungi, Lichens, and the cells
of fleshy leaves and fruits are very soft ; while the cells of many
woods, ¢. g., in Palms and Tree Ferns, and those of the albumen
of many fruits, exhibit a bony hardness; and finally, the cells of the
epidermis of Equwisetum and Calamus possess such solidity, that
it scratches metal, and strikes fire with steel.

All membranes are readily penetrated by water, and in the
operation become more or less softened and swollenup. The latter
phenomenon occurs in a higher degree the younger and softer the
cell is; whether, however, as Schleiden states, the membranes of
nascent cells are actually soluble in water, is more than doubt-
ful to me. The swelling up occurs strongly in many thick-walled
cells which in a dry condition have a horny consistence, as in
Lichens, Fucoide, and in certain gelatinously soft celis (the so-
called collenchyma cells) lying beneath the epidermis of herbace-
ous plants. In the short parenchymatous cells no great difference

s

10 ANATOMY AND PHYSIOLOGY OF

appears to occur in the strength of the expansion in the different
directions; but in the elongated cells of the bast and wood, the
swelling up resulting from moistening takes place principally in
the direction of the breadth, and only in a very small degree in
the longitudinal direction.

The cell-membrane of young cells is completely colourless and
transparent ; in full-grown cells it is frequently imbued with yel-
low, red, or brown colouring matters, whereby in many cases the
transparency is importantly interfered with. This alteration is
very striking in the change of the sap-wood into heart-wood, for
im many trees, e.g. in the ebony and yew, the white is converted
ito a more or less dark colour, without the cell-membrane in-
creasing in thickness, while at the same time it acquires a far more
considerable solidity and independence of the influence of mois-
ture. .

Observ. Tt is difficult to conceive how some phytotomists (Link, “Z#le-
ment. Phil. Bot.” 1824, p. 366; Meyen, “ Physiol.” i. 30) came to the opinion
that cells contract in the direction of their length when moistened, and
again expand when dried, since, on the contrary, all cells expand in every
direction when moistened. In the elongated cells of the wood the con-
traction by drying in the direction of the length is, of course, but small,
yet it occurs constantly. In wood of Dicotyledons the longitudinal con-
traction from the wet to the perfectly air-dried condition amounts to only
0-072 to 0-4 per cent., while the contraction in the direction of the breadth
is as muchas 4 to 9 per cent. According to Schleiden’s experiments, the
bast-cells of flax expand only about 0-0005 to 0-0006 ; but he considers
it possible that there was an important error here (Beitrdge, i. 69). Ac-
cording to the researches of Ernest Meyer, the Manilla hemp (Phor-
mium ?) expands, when wetted, about 1-50th of its length, while the
increase of breadth amounts to 1-5th.

6. Structure.

In examining a transverse section of a thick walled cell, e. G-,
of wood-cells of Cle-
matis Vitalba, the
bast-cells of Palms,
(fig. 11), or the thick
walled pith -cells of
Hoya carnosa, (fig.
12) we find by strong-
ly magnifying, that
the cell-membrane ig
not homogeneous, but
composed of numer-

és ous super-incumbent
“ihohbercolsofCosnr be walled color me nue? ek Jayers coneentrical-
tryophora. curnosd. ly surrounding the
cavity of the cell. By the action of a mineral acid of proper

THE VEGETABLE CELL. li

degree of concentration the membrane is caused to swell up, its
lamellar structure becomes very much more distinct, and a great
number (often fifty) of separate layers may be detected. By this
means the lamellar structure may be demonstrated even in those
cases in. which the unaltered membrane appeared completely homo-
geneous ; for instance, in the horny cells of the albumen of Phy-
telephas. Usually the wall of the cell is of equal thickness on
all sides ; in this case the layers run uninterruptedly round the
cavity and form perfect cells encased one within another. In
many cases (¢. g., very frequently in the epidermis-cells—fig, 13—
and in the brown cells which
surround the vascular bundles
of the Ferns) the different sides
of the cell possess, on the con-
trary, a very different thick-
ness ; in this case the layers of
the thicker portion of the wall
are not continued over the thin
sides, but are bevelled gradu-
ally off.

This condition alone allows
us to conclude with great pro-
bability, that the growth of
the cell-membrane in thickness
does not depend upon the thin
membrane of the young cell it-
self growing thicker by the absorption of new cellulose, but that
it arises from a periodical deposition of new membranes upon the
already completely developed wall. But the complete confirmation
and more accurate knowledge of this process are only obtained
through the circumstances next to be mentioned.

The wall of young cells having yet very thin membranes, ap-
pears perfectly smooth and uniform ; but if the tissue of the same
organ is examined at a later period, the walls of its cells are found
to have become thickened ; these walls are almost without excep-

Cells of the Epidermis of the stem of Visewm album.

tion found to be covered with a greater or smaller number of pore-.

like points or slits, which are distinguished by the name of dots
(tiipfel or pits). A more minute examination of the cross-section of
the cells (figs. 11, 12) reveals that these spots are formed by canals
which open freely into the cavity of the cell, but are closed externally
by the outermost thin membrane of the cell. When all these cir-
cumstances are taken together, it becomes most indubitably evi-
dent, that the primary membrane of the cell is completely closed
and not possessed of visible pores ; that the subsequent deposits,
on the contrary, have the form of perforated membranes, and
that the deposition of these secondary membranes takes place in
the direction from without inwards upon the inside of the primary
membrane.

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seen aa te Ee NR NA TNE REND cate ne eee chiens SH su pemnpyconienam ere =< = 2 = =

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pay ANATOMY AND PHYSIOLOGY OF

Observ. It isnow no longer worth while to give an historical review
of the opinions that had heen expressed as to the structure of the cell-
wall and of the spots, before the appearance of my essay “On the Pores of
Vegetable Cellular Tissue,” in 1828. But it is necessary to advert to the
objections which have recently been advanced by Harting and Mulder
against my doctrine of the structure of cells, and of the gradual and
successive deposition of the secondary layers from without inwards.
(See Harting “Mikrochem. Onderzoekingen,” &c., in the “ Lidshrift voor
naturlijke geschiedents,” XI.) (translated in the Linnea XIX. Harting :
“ Letter to H. v. Mohl,”— Bot. Zeitung, 1847, 337.—Maulder “ Physiological
Chemistry.” —Mohl “On the Growth of Cell Membranes,’—Bot. Zeitung,
1846, 337.) TI believe I may safely leave unnoticed the objections ad-
vanced by Hartig. (“ Beitrdge zur Entwickelungsgesch. der Pflanzen,”
1843; “ Das Leben der Phlanzenzelle.” )

Mulder and Harting attack my theory on both anatomical and chemi-

‘cal grounds, and seek to demonstrate that the cell-membrane increases in

thickness in the direction from within outwards by the deposition of
layers upon the outside of the original membrane, which process of growth
is followed, in some cases, by a deposition in the interior of the cavity of
the cell, while in particular instances (in the cells of horny albumen) the
membrane itself grows thicker by the interpenetration of foreign matter.
In the first place, my opponents deny that the thin membranes of the
young cell are imperforate, and that only the subsequently internally
deposited layers are porous, since they, on the contrary, believe, that they -
found the membrane of young cells to be perforated like a sieve, while a
perfectly closed membrane is deposited subsequently on the outside of
these closed cells. It is, of course, not for me to decide who observed most
correctly, I or Harting ; but I must stand by the facts I have stated, and
do not believe that Harting would have been deceived in the manner he
has, if, instead of selecting only cells having small pits for his observa-
tions, he had extended his researches also to cells with large pits, between
which the secondary membranes appear in the form of narrow fibres ; and
had properly regarded the analogy which exists between the structure of
the vascular utricles and cells. Harting finds a second reason for hig
view of the external growth in his micrometrical measurements of young
and of thickened cells (Linnea, 1846, 552), by which he arrived at the
conclusion that the cavity of the wood-cells expands during the increase
of thickness of a’shoot, in exactly the same proportion as the unlignified
cells, whence he argued that the thickening of their walls is to be ascribed
to a deposition taking place upon the outside of their primary membrane.
On the other hand, I consider that I have demonstrated by my measure-
ments (“ Bot. Zeitung,” 1846, 358) that exactly the contrary occurs, and
that the thickening of the walls is combined with a narrowing of the
cavity of the cell_—-Mulder and Harting deduce a third counter-evidence
from the chemical reaction of the cell-wall (which will be spoken of here-
after). The membrane of young cells is coloured blue by the action of
iodine and sulphuric acid ; in full-grown cells this very often happens only
to the innermost layers, while the intermediate acquire a green or yellow,
and the outermost membrane a brown, colour, altogether withstanding the
solvent power of sulphuric acid, which is not the case with the interme-
diate and inner layers. From this my opponents draw the conclusion

THE VEGETABLE CELL. 13

that the membrane of the young cell and likewise the inmost layers of
full grown cells are composed of cellulose, the intermediate and outermost
layers, on the con-
trary, of other com-
pounds, which are
subsequently form-
ed and deposited on
the outside ofthe cel-
lulose membrane,
Against this I have
shewn. (“Botanische
Zeitung” 1847,497)
that the chemical
researches by which
their deductions are
supported, were im-
perfect; that the
outermost layers of cell-membrane are composed in like manner of cellu-
lose, but are infiltrated with foreign compounds, which prevent the re-
action of iodine and sulphuric acid; that the date of origin of a layer
must not be deduced from the che-

mical reaction, since both the inner Fig. 16.

and outer layers may undergo a che- ‘

mical metamorphosis, which does not ee

stand in any connexion with the time Ss a

of its origin; and that therefore ana-

tomical grounds alone can serve for

the decision of the order in which dif-

ferent layers have been developed.—

Lastly, in reference to the statement

that the thick walled cells of the

albumen of Phytelephas, Iris, &e.

(figs. 14, 15), and the so-ealled col-

lenchyma cells (fig. 16) possess uni-

form, and not lamellated, walls, and

that consequently their primary mem-

brane itself has increased in thickness ; Cells from the leafstalk of Nymphea alba.
this assertion depends simply upon im-

perfect investigation. If the authors had treated these cells with sulphuric
acid of the proper degree of concentration, they would have found the
lamellation.—In short, the researches which I was caused to undertake
by the objections of Harting and Mulder, served only to strengthen the
grounds on which I had built my theory of the growth of cell-membranes.

Cells of the albumen of Sagus tedigera.

The secondary cell-membranes deserve a separate mention. Taken
altogether, it is seldom that they appear to the eye, as the primary
membrane does, in the form of an uniform smooth pellicle, ag it
were a hardened mucilage, for example i the Conferve and in
many hairs. Whether in such a case they are really devoid of
special structure, is doubtful, for such cells) when drawn out
lengthways, sometimes tear in an oblique direction, so that they

Ti en 2: te sean tee imran a serie

It ANATOMY AND PHYSIOLOGY OF

may be more or less perfectly drawn out into a spirally wound
band. This phenomenon, together with the visible conditions of
structure, to be spoken of directly, appear to me to indicate that
the secondary cell-membranes, without being composed of actual
primitive fibres (which cannot in any way be demonstrated), pos-
sess indeed a fibrous structure, since their molecules are connected
more firmly in the direction of a spiral than In any other direc-
tion. (See “On the Structure of Vegetable M embrane,” in my
“Vermischte Schriften.” )

Next to these cells, appearing perfectly homogeneous to the eye,
come such as exhibit a very fine spiral streaking of their mem-
brane, as is the case in the cells of many woods, ¢. g., in Pinus syl-
vestris, and in a very striking degree in the bast-tubes of the Apo-
cyneze and Asclepiadee, e.g., in Vinca
(fig. 17), Ner'wm, Ceropegia,and Hoya.
Although in many of these cases also the
membrane has the aspect of being com-
posed of separate fibres lying very close
together, yet this appears actually not
to be the fact, but the streaking to be
dependant upon the unequal thickness
or density of the different parts of a

B. A picce of the same, connected membrane. In favour of this
more highly magnified. i. in particular, the circumstance, that
in the bast-fibres of the Apocynese, the spiral is wound
sometimes to the right, sometimes to the left, in the
superincumbent layers of the same membrane; the ap-
parent fibres, therefore, then cross, a condition of which
T know no example in the actual division of the se-

condary membrane into fibres.
In other cases occur, instead of the streaks, perfect
slits running in a spiral direction, by which the second-
ary layers become divided into broader or narrower
A. Liber-cell of bands (fibres), running parallel with each other. The
Vinea major. direction of the spiral in which the fibres run is, as a
rule, the same in all the cells of a tissue ; therefore the fibres of
two contiguous cells cross upon their two coherent walls. In the
overwhelming majority of cases the fibres are wound to the right
(in a botanical sense, 2.¢., therefore in the manner of a left-handed
screw). Instances of the contrary do certainly occur, sometimes
merely as isolated cases in particular elementary organs, some-
times regularly in particular specimens of a plant. Such spira
fibres occur in rarer cases in the common parenchymatous cells of
the stem and leaf-stalk ; for example, to a very remarkable extent
in various species of Nepenthes, in many Orchideze ; on the other
hand, they are more frequently confined to special organs, for in-
stance to the elaters of the Hepatics, the cells of the sporangium
in Equisetwm (fig. 18), a portion of the cells of the leaf and the

THE VEGETABLE CELL. ' 15

cells of the cortical layer in Sphagnwm, the hairs in the Cactacez,
particular layers of the seed-coat in Caswarinu, Salvia, many Po-
lemoniacese, &e., and in many plants to the anther-cells. Parti-
cular organs composed of such fibrous cells, not unfre-
quently possess a spongy, soft consistence, e.g. the Fig. 18.
outer rind of the root of many tropical Orchidaceze and
Aroidez, the sepals of Jllecebrwm verticillatwm, the
pericarp of Cachrys Morisoni, C. odontalgica, the ribs
of the fruit of @thusa Cynapiwm.
The annular fibre (fig. 19) which runs in a trans-
verse direction on the cell-wall, crossing the longitu-
dinal axis of the cell at right angles, is to be regarded
as a slight modification of the spiral fibre. It not un-
frequently occurs alternating with the spiral fibres in
_ the same cells as the latter, ¢.g., in the cells of many &
anthers, in the sporangium of the J ungermannie, and
in the leaves of Sphagnum. It may be regarded as a
middle form between the right and left wound spiral
fibres. Cell trom the
The reticulated structure of the secondary mem- Se
branes occurs infinitely more frequently than the regu- vense.
lar spiral formation, and scarcely a plant can be found, 1
from the Mosses upward, in which this structure cannot be more
or less clearly distinguished in the majority of its cells. Some-
times, but in comparatively rare cases, the secondary membranes
of the reticulated cell resembles those of the spiral-
fibrous cell, in that they are likewise divided by closely Fig. 19.
adjacent pits into narrow fibres, which fibres, however,
do not run in a spiral direction, but are connected into
a more or less regular net, with narrower or wider,
roundish or angular meshes, ¢. g., in the cells of the
wing of the seed in Swictenia, of the pericarp of Pi-
cridium tingitanum, P. vulgare, in the seed-coat of
Cucurbita Pepo, of the parenchyma of the leaf of Sanse-
viera guineensis (fig. 20), in isolated cells of the pith
of Rubus odoratus, Erythrina Corallodendron. But
in the great majority of cases the secondary membrane
is perforated by comparatively small orifices at few
points only, and therefore does not appear under the
form of a net-work of narrow fibres, but as a connected
membrane perforated like a sieve. Since this is the Qo), mom =e
usual condition, which occurs in almost all cells (see sporangium of
fig. 7), it will be unnecessary to cite examples; yet joiymomne.
it may be permitted to name some particularly charac-
teristic cases, the investigation of which prepares the way to a com-
prehension of less distinct structures, e.g., the parenchymatous cells
of the leaf-stalk of Cycas revolyta, the thick walled pith-cells of
Hoya carnosa (fig. 12), the cells which form the stony conere-

RANA ae apne ANP RPTINND tt ihc SA SEE ae ae aE see

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A se ee
a eg ig es NL

seen tne naeemnt me anette A

16 ANATOMY AND PHYSIOLOGY OF

tions in the flesh of pears and quinces, the horny albumen of Phy-
telephas, of many Palms (fig. 14), and of the Rubiaceze. These
smaller orifices in the secondary membrane are denominated pits,
the cells themselves pitted cells. The numerous transitions from
this form of cell into the form of those hav-
ing a net-work of narrow fibres, and from
these into the spiral-fibrous cells, furnish
the evidence that the fibres are not, as
earlier phytotomists believed, to be consi-
dered as a peculiarly organized elemen-
tary portion, but that they are nothing
else but narrow sections of the secondary
membrane lying between elongated pits ;
that between fibre and membrane there
exists a distinction in form, but none in
essential nature.

The distribution of the pits upon the
cell is usually altogether irregular, espe-
cially upon the horizontal transverse walls
ofthe parenchymatous cells. On the other
hand, it is common, and especially in elon-
gated cells, for the pits upon the lateral

walls of the cells so far to exhibit regu-
larity in their position, that they stand more or less exactly in the
direction of a spiral, and are frequently drawn out lenethways in
this direction (fig. 21), so that they appear as short
Hig. 21. slits. Sometimes also a certain rule may be met
[}-~~\-}7 with in reference to the places on which pits exist
S® or are deficient. Thus in the wood-cells of most
Se Conifersee they are found on the side-walls, turned
CS towards the medullary rays; thus in loosely con-
eae nected parenchymatous cells they not unfrequently
Ss occur on the flattened parts of the walls by which
(3) the cells are coherent together, while they are ab-
een sent from the surfaces which bound the mter-cel-
lular passages, as occurs frequently in the cortical
cells of Dicotyledons ; or, if they occur on the inter-
pa Ba cellular passages, they differ in size and form from
eee oe those situated on the side-walls of the cells, e. 9,
soba "9 in Cycas, in the wings of the seeds of Swietenia.
The pits are moreover usually wanting to the
outer walls of the epidermal cells, but they may also occur here ;
as, for example, on the leaves of Cycas.

The pits of one cell are most intimately connected in regard. to
form and position with those of the contiguous cell; and it is a
general law, that when two pitted cells are coherent together, the
pits of the two cells lie exactly opposite to each other ; so that in
very thick walled cells the cavities of the two cells are only sepa-

Cells of the leaf of Sanseviera
guineensis.

THE VEGETABLE CELL. Ly

rated from each other, in the canals of the pits, by the primary
walls, which form a very thin partition (figs. 11, 14,15). This
dependence of the structure of one cell upon that of its neighbours,
becomes the more prominent the more the reticulated formation
prevails in the secondary membranes, and it disappears in propor-
tion as the spiral structure becomes more distinctly evident.
Therefore where the pits are scattered irregularly they correspond
accurately in form and position ; where they are arranged in a
Spiral direction, and present the appearance of short elliptical slits,
they correspond in position but no longer in form, since being situ-
ated obliquely in the opposite direction, they cross and only cor-
respond at their central portion (fig. 21). Finally, when the pits
are extended into long spiral slits, surrounding the cell, the rela-
tion to the contiguous cells has altogether disappeared.

In thick walled cells the pits usually form cylindrical canals,
which, however, frequently open into the cavity of the cell by a
funnel-shaped opening at their inner extremity; and sometimes
the outer blind end is somewhat enlarged. Not unfrequently-two
or more pit-canals unite into one common passage, opening into
the cavity of the cell (fig. 12). .

In many cases the primary walls of two contiguous cells sepa-
rate from each other at the spots where the pits lie and leave a
lenticular cavity between them, which has a rather larger circum-
ference than the
pit itself (fig. 22)
and then ap-
pears like a ring
surrounding the
pit (fig. 23). I am
only acquainted
with this struc-
ture in elon-
gated cells; itis *
most distinct in
the wood - cells
of the Coniferze Us ‘
and«. C cadeze, ransverse section through a pee pecsceh etcae sent oe
but it sak in fi pit (a) of enue Poa ee pe a aa
the wood - cells
of many Dicotyledonous trees. These cavities are not yet existent
in very young cells, but they are found before the deposition of
the secondary membranes, and the formation of pits arising out of
this. Schleiden’s assertion that these cavities arise from the secre-
tion of a bubble of air between the previously blended cell-walls is
incorrect ; they are filled with sap in the young condition of the cells.

In isolated, but very rare, cases, the primary membrane which
is stretched across the pits as a partition, becomes absorbed after
the completion of the development, whereby the pitted cells be-

c

— ‘coeunain, ae
= ee

as
ae

cali wat ote -
aeciiitene cit SN

18 ANATOMY AND PHYSICLOGY OF

come converted into porous cells. This occurs most remarkably
in certain Mosses, especially in the fibrous cells of Sphagnum,
the leaf-cells of Dicranum glaucum
Hig. 24. (fig. 24), and Octoblepharum albidum,
&e. (See “Anatomical researches on
the Porous Cells of Sphagnum” in
my “Vermischte Schriften,’ 294; also
Schleiden, “ Beitréige,” i. 71.) This phe-
nomenon is very rare in the Phanero-
gamia; I found it decidedly in fibrous-
cells, ¢.g., in the rind of the root of
Epidendrum elongatwm, in the seed-
ye Se coat of Martynia, &c., &e. Whether
it occurs normally in the wocd-cells
of Pinus, as Unger asserts, is yet a matter of doubt to me.

In the generality of cases, all the layers deposited on the inside
of the primary membrane agree completely in their form, so that
there is no reason why we should adopt a further division of the
layers than that into primary and secondary membrane. But in
particular cases, the secondary membrane consists of two layers of
strikingly different structure, so that it becomes necessary to dis-
tinguish between primary, secondary, and tertiary membranes.

To what extent such a distinction into secondary and tertiary
membrane exists, cannot be stated in the present state of our
knowledge. I must, therefore, confine myself to the mention of
certain examples in which the existence of the tertiary membrane
may be demonstrated with certainty. To these belong the wood
cells of Tawus and Torreya, the primary and secondary mem-
branes of which are formed exactly as in the wood-cells of Pinus,
but their cavity is lined with an inner membrane, which is covered
with a fibre-like thickening running in regular spiral lines (fig. 25).

The same structure is repeated in the wood-
cells of certain Dicotyledonous trees, ¢.g., in
Viburnum Lantana.

The contrast between the secondary and ter-
tiary membranes is most striking in cells which
occur in the coats of the seeds of very various
plants, and in which one of the inner mem-
branes is split into spiral fibres; while the
other consists of homogeneous layers, which
when wetted with water swell up so strongly
that they burst the primary membrane. This

Wood-cells of Taaus property is generally found in the secondary

layers, while the tertiary membrane appears
as a spiral fibre, ¢.g., in the outer cells of the seed-coat of Collomia
and other Polemoniaces, of the pericarp of Salvia, in the hairs of
the fruit of Senecio vulgaris, &¢.; in other cases the secondary
membrane is formed of spiral fibres, and the tertiary layers con-

THE VEGETABLE CELL. 19

sist of the substance capable of swelling up, ¢. g., in the hairs of
the seed of Ruellia strepitans.

Observ. 1. Hartig, who first discovered that the tertiary membrane in.
Taxus possessed the form of a connected pellicle and was not composed of
fibres, propounded the doctrine (“Beitrage zur Lntwicklungsgesch. der Rflan-
zen,” 1843): that such an inner coat, which he called the ptychode, occurred
in all cells) He thought that this membrane was distinguishable from
the intermediate layer (his Astathe) by definite chemical characters, since
it was not coloured blue by iodine and sulphuric acid, like the latter, and
agreed in this character with the outermost coat of the cell (which he
called the Hustathe). Hartig considered this inner layer as the oldest, the
outermost the youngest, of the cell-membranes. The whole of this doc-
trine depends upon very imperfect observations. The tertiary membrane
of Taxus is composed of cellulose, it is therefore a true cell-membrane ; but
Hartig seems, in many other cases, to have taken the primordial utricle
(subsequently to be described) for a layer of cell-membrane, and thus to
have classed together structures which have nothing at all in common.

Observ. 2. It may not be out of place, after this exposition of the struc-
ture of the secondary membranes, to cast a glance at the structure of the
vascular utricle, since the different modifications of the structure of the
cell-wall are met with again in the vessels, and, indeed, in many cases dis-
played much more distinctly than in the cells, so that these conditions
were observed in the vessels long before they were known in the cells,
albeit much that was incorrect was stated of them. The vessels were ’
divided according to the modifications of the structure of their secondary
layers, into spiral, annular, reticulated, dotted vessels, &c.

The most widely distributed form is the spiral vessel, for this occurs in

all plants which
fig. 27. Mig. 28. Fig. 29. possess vessels ; and
particularly,in most
organs the first ves-
sels which appear
belong to this form,
so that they are met
with in the hind-
most parts next the
pith, of the vascu-
lar bundles of the
stem. The secon-
dary membrane of
these vessels is di-
vided into one or
more (in Musa as
/| many as 20) paral-
which as a rule ter-
minate in an annu-
Spiral vessels of Sambucus lar fibre at theupper
Ebulus. and lower ends of
the vascular utricle.
If the vessel is developed in an organ which has already completed its
o 2

Saeeaenenececnsonmcnatansaenaces

20 ANATOMY AND PHYSIOLOGY OF

longitudinal growth, the turns of the spiral fibre lie close together (fig.

27); but if the organ undergoes elongation after the completion of the
development of the vessel, the turns of the fibre are drawn far apart (figs.
28, 29), by the stretching which the vessel suffers ; consequently, very _
loosely wound spiral vessels are usually found in the posterior first-formed *
portion of the vascular bundle, nearest to the pith, while those lying nearest
the bark have close convolutions.

The annular vessels (fig. 30) form a slight modification of the spiral
vessels, for in many cases a series of vascular utricles containing spiral
; fibres are regularly found followed in the same vessel

by a series of utricles which contain annular fibres, or
_ spiral fibres and annular fibres alternate without any
definite rule, often in the same vessel.

~The reticulated vessels occur in manifold modifications,

in particular among the vascular Cryptogamia, and in
the outer youngest parts of the vascular bundles of the
Monocotyledons. In these occurs a dependence of the
form and distribution of the pits upon the formation of
the adjacent parts, similar to that which we have found
in the pitted cells. When several vessels lie immedi-
ately upon one another, the walls by which they are
coherent together (fig. 31, #) are covered with trans-
verse pits, separated by narrow fibres, and these pits
occupy the whole breadth of such a side-wall, but are
not continued over the angles at which the several

* lateral faces of the vessel meet. To this form is applied

stem ep wom the the term scalariform ducts. But if the wall of such a
. . ? . e .

containing both vessel is in contact with cells by a large or small surface

mings are Pl (fie. 31, b) its pits exhibit the elliptical or rounded form

re.
of the pit of the cells, and are sometimes distributed

quite irregularly, sometimes arranged in a spiral direction, and the vessel
retains the name of reticulated. Very frequently the same vessel exhibits
both these modifications of structure at different points.

Lastly, the pitted vessels (fig. 32) which occur in the wood of Dico-
tyledons (with the exception of its
oldest parts, in contact with the pith)
exhibit on those points of their walls
by which they are in contact with a
second vessel, a more or less abundant
quantity of pits surrounded by a line,
while the walls bordering on cells pre-
sent the form of reticulated vessels,

| 4. @, possess pits without a boundary
line, or are quite devoid of them. In
some cases, for example in the Lime, a
tertiary membrane occurs in the pitted
vessels, which appears in the form of

fibres running between the pits.
ee om pes eee as The septa between the vascular utri-
cles do not always become perfectly

absorbed ; but in the reticulated, and especially often in the pitted vessels,

AB

THE VEGETABLE CELL, 21

secondary layers are deposited in the form of a net-work, or of parallel
cross fibres on the transverse or oblique partitions of the vascular utricles,
while the primary membrane is regularly absorbed between. these fibres,
so that the open communication between the vascular utricles is not
interrupted.
Observ. 3. In the description of the structure of the cells and vessels,
I have mentioned the spiral and reticulated course of the fibres as two
distinct modifications of the structure of the secondary membrane. Since
transitions between the two structures frequently occur (fig. 33), and
since when the fibre is reticulated the pits are arranged more or less dis-
tinctly in spiral lines ; since, moreover, the pits scattered over an uniform
membrane frequently have a longish form, and their long diameter like-
wise situated in an oblique spiral direction, the thought readily presents
itself that spiral structures form the basis of secondary membranes of all
cells and vessels, and that the other forms owe their origin to subsequent
transformation of the spiral cell and spiral vessel. The view has been
expressed by most phytotomists in reference to the
Fig, 33. vessels ; but the conceptions that have been formed
Y: of the processes occurring in this metamorphosis
were for the most part of rather a rough character.
Thus the notion was extensively embraced, that the
spiral fibre could not follow the expansion which
the vessel underwent during its growth, and tore up
into fragments, which again united into rings, and
thus brought abowt the formation of annular vessels.
Completely as this idea, which was a contradiction
to all observation, had been refuted by Molden-
hawer, it remained a standing article in all phy-
totomical writings up to “ Meyen’s Physiologie.”

Schleiden (“On the Spiral Structures in the Vege-
table Cell,” Flora, 1839) sought to explain the origin
of the annular vessels from the spiral vessels in a
manner less easy to refute, assuming that in each
case two turns of a spiral fibre grew together into a

ring, while the rest of the fibre, running between
petro gut het veac rings was subsequently dissolved. My own

hybridum. observations (“On the Structure of the Annular Ves-

sels,” in my “Vermischte Schriften,” 285) compel me

to declare most decidedly against this explanation, since they demonstrated

the rings to be primeeval, original structures, from their very first appear-

ance, and the seeming transitional stages from spiral vessels into annular

vessels to be permanent intermediate forms between the two kinds of
vessels.

The idea that the reticulated vessels are produced from spiral vessels
has been more extensively defended, and especially lately by Schleiden
and Unger (Linnea, 1841, 394). Nothing appeared simpler than the
assumption that cross fibres were formed between the convolutions of the
spiral fibre, and that the spiral was thus converted into a reticulated
vessel, But two circumstances lead me to reject this notion. most de-
cidedly. In the first place, observation of the vessels in which the second-
ary layers have just begun to be formed, gives evidence that the delicate

ee

ip ANATOMY AND PHYSIOLOGY OF

fibres first deposited are already connected into a net-work, as is especially
seen in the examination of the young roots of the Palms. On the other
hand, this conception of the transition of a spiral vessel into a reticulated
vessel is incompatible with the mechanical condition of the fibre. When
swo spiral vessels lie upon one another their fibres must cross, since in the
majority of cases the fibres of the two vessels run in the same direction
(homodromous) ; but we find that when two reticulated vessels lie against
one another, the fibres in the two vessels are placed transversely, and cor-
respond accurately together in position; which could only result from
the fibres of the two vascular utricles losing their original spiral direc-
tions, and one being pressed down to the right, the other to the left, until
their situations should exactly correspond. Who will believe im such a
motion of fibres, which are not free but adherent to the vascular utricles,
themselves coherent together? and who has seen anything of the kind?
A process of this kind might be held to be possible so long as we were
ignorant of the true structure of the vessel, and believed that the fibre
lay free in the cavity of the vessel, an error which formerly prevailed ex-
tensively, and which one would not have expected to have still met with
in a writing of Schleiden’s (“ Betériige,” i. 188). And if the incredible
statement, that the fibre performed such a journey over one side of the
vessel, were actually assumed to be true, how should the prolongations of
it over the other sides of the vessel behave? Would these tear away or
be pulled backwards and forwards, to restore by their more oblique posi-
tion what was lost in their spiral course over the other side? Instead of
the confusion which must necessarily arise from this, we meet with the
most beautiful order. If the lateral walls of the vessel are in contact
with cells, we find its pits corresponding with those of the cells ; 1f one
part of a vessel is connected with another vessel we meet with horizontal,
slit-like pits. Thus we see clearly that one elementary organ influences
the organization of an adjacent one in a definite manner, but we are no-
where able to observe, that an organ already developed to a certain extent
allows its already organized parts to perform movements in order to place
themselves opposite the parts of the neighbourmg organs. Since none of
these matters can be seen, the processes are referred back by Schleiden to
a time at which the observation is impossible. Thus he says (“ Grunda.
der wiss. Botanik,” i. 228 ), it seems to him very probable that the spiral is
in existence long before it is visible under our optical instruments, since it
is composed at first of a substance which does not differ optically from the
cell-wall and cell-contents ; hence, many forms might be referred to the
spiral only at that epoch, if we assume that the intermediate stages were
run through before the structure was yet visible. I readily allow the
author to speculate as to the course of fibres which cannot be seen, but I
must be excused from following him into this region. Valentin, indeed, who
originated the theory of the expansion of the spiral fibres in all directions
(“Rep. f, Anat. and Phys.” i. 88), believed that this could be demonstrated
by observed facts, for he stated that he had found the secondary mem-
brane making its first appearance in the form of a granular substance, the
granules of which at first exhibited no definite order, but were subse-
quently arranged into spirals, and became connected into the spiral lines
which might be distinguished on the completely formed membrane ; a
view which has not acquired confirmation from any subsequent observer,

THE VEGETABLE CELL. 23

It is scarcely worth mentioning that, Meyen (“ Physiologie,” i. 45)
set up the theory that not only the secondary layers, but also the primary
membrane was composed of distinct spiral fibres grown together. He
was led to this opinion principally by the cells containing a very fine
spiral fibre, of a Stelis gathered by him in Manilla, the structure of which
he completely misapprehended, since he imagined that the fibres formed
the primary membrane, while they belonged to the secondary.

In conclusion, it may be remarked that Schleiden’s hypothesis (“ Bei-
trdge,” i. 187), that in the formation of the secondary layers there exist at
first, at least, two spiral bands, one corresponding to the ascending current,
the other to the descending current of the mucilaginous formative sub-
stance, the two extremities coalescing at the ends of the cell, and that in
most cases these become blended together at a very early period, is simply
to be banished into the region of dreams.

The opinion which formerly prevailed widely, and which Link (“ Phil.
Botan.” 1837, i. 177) still defends, that the pits of the scalariform ducts
and pitted vessels are the remnants of the fibres of spiral vessels broken
up into fragments, requires no further refutation. Holes in a membrane
can scarcely be considered as elevations.

Observ. 4. In the preceding I have spoken of cells and vessels as clearly
separated organs, because in most plants the fully-developed cell differs in
a marked manner from the fully-developed vessel; but it must not be
forgotten that transitional structures occur. One form, the porous cells,
has already been mentioned ; these come near to the vessels in the large
open pores, by which they communicate with each other, but they are dis-
tinguished from those by the fact, that they form a parenchymatous tissue
in the manner of cells, lie upon the surface of
organs, and, in part, in Sphagnum (fig. 33, B), Fig. 33, B
open even to the external air ; while the vascular a
utricles are always combined into tubes, which
run among the cells in the interior of plants.

Another intermediate structure occurs in the vas-
cular Cryptogamia, particularly in the Lycopodia
and Ferns, as well as in the Conifere and Cyca-
deze. In these plants we meet with the peculiar
condition that the wood is not composed of a
mixture of elongated cells and vessels, but of ele-
mentary organs of one kind, which resemble pro-
senchymatous cells in their form, and vessels in
the structure of their walls, and give evidence of
their near relation to the latter, in the fact that
the prolongations of the vascular bundles of the
stem entering into the leaves, contain perfectly
developed vessels ; as also in the fact, that in the
stems of Conifer and Cycadez, the innermost
elementary organs, bordering on the pith are per- Porous cell furnished with
fect spiral vessels, and that in Zphedra particular ae ae Le
wood-cells become united into perfect pitted ducts.

Observ. 5. Perhaps it is not altogether superfluous, in reference to the
terminology of the pitted cells and vessels, to remark that since the struc-
ture of the pits (tipfel) and their distinction from actual holes have been

24 ANATOMY AND PHYSIOLOGY OF

understood, it is the more general custom to apply the term pit (¢iipfel )
to the canals perforating the secondary layers, and closed externally by
the outer membrane of the utricle, and the term pore to the same canals
when the primary membrane has been absorbed and the orifices of the
utricles open freely into each other. Schleiden, on the contrary, uses the
name of porous instead of pitted (getiipfelten) cells, calls the pits pores,
and the pores holes (lécher), because (“ Beitrige,” i. 189) according to
Adelung and Heinsius, the word tiipfel (dot) means a shallow depres-
sion, or a slightly elevated spot upon a surface. I will not enter into
any etymological controversy against such authorities, but keep simply
to my Swabian German, and am consequently of opinion that a panther’s
skin is getiip/t (spotted or dotted), although its spots are neither depressed
nor elevated.*

c. Chemical Conditions.

The basis of the membranes of all the elementary organs of
vegetables consists of neutral hydro-carbons; in almost all cases,
and perhaps without exception, of cellulose.

Cellulose is colourless, insoluble in cold and boiling waiter,
alcohol, ether, and dilute acids, almost insoluble in weak alkaline
solutions, soluble in concentrated sulphuric acid ; it is converted
into dextrine by dilute sulphuric acid at a boiling heat. When
imbued with iodine it becomes coloured indigo blue if wetted
with water, this colour appears more readily under the conjoined
influence of water, sulphuric acid, and iodine, According to Payen,
the formula of its composition is C12 Hap Oxo.

Cellulose probably does not occur in a pure condition in any
cell-membrane, since a series of both organic and inorganic com-
pounds are deposited within it ; in which fact is to be sought the
explanation of the manifold physical and chemical differences
which are exhibited by the membranes of the same cell at different
periods of their age, as well as by the cells of different plants.

The combination of cell-membrane with inorganic substances ig
a very general condition, for the only examples of exception to
this which have as yet been met with, are a few species of Mould
Fungus (Mulder), into which, however, ammonia might still have
entered as a substitute for the fixed bases. In all other plants a
skeleton (the ash), corresponding to the form of the membrane,
and composed of the alkalies, earths, and metallic oxides which
had been deposited in it, remains behind after the cell has been
burnt. The younger an elementary organ is, the more abundant,
in general, the alkalies appear to be; the older it is, the more
exclusively the earths and metallic oxides seem to be combined

* Gome confusion exists also in our English terminology, the terms
dotted and pitted tissues are indifferently applied to these structures, called
by the Germans getiipfelt. I have used the word pitted throughout this
translation to express this term, because it indicates the true structure.

—A, H.

THE VEGETABLE CELL. 25

with its substance. The higher the degree in which the latter
occurs, the harder the membrane becomes, as is shewn by the
relation of the heart-wood to the sap-wood, and in a still greater
measure in many seed-coats of a bony consistence, e.g., the peri-
carp of Lithospermum, which contains much lime, the epidermis
of Hquisetum and Calamus, in which a great quantity of silica is
deposited. However, we are without any accurate knowledge of
these conditions, in spite of the countless analyses of ashes which
we possess, for these give the product of ash of the cell-contents
_ and cell-membrane together.
The deposition of organic substances is not less general than
that of inorganic compounds, at least in particular layers of cell-
membrane. Among these the nitrogenous compounds are cer- ;
tainly the most widely distributed. They do not occur in the |
membranes of cells which are just at the commencement of therr |
development, for these are not coloured yellow by tincture of |
iodine, yet scarcely a full-grown cell is met with in which this is
not the case. That these nitrogenous compounds belong, in many
instances, and especially in the cells of the wood, to the series of
proteine compounds, we have evidence (as Mulder poimted out) in
the violet colour which hydrochloric acid produces after long oper-
ation, and in the yellow colour which ammonia produces after a
previous action of nitric acid. The presence of these compounds
explains how, according to Chevandier’s analysis, wood contains
0-67 to 1:52 per cent. of nitrogen. The

darker yellow a cell-membrane is co-

loured by nitrogen, the more firmly it

withstands the action of sulphuric acid,

and the more difficult it is to obtain the

blue colour by the combination of this

and iodine. In most parenchymatous

cells, especially in the thin walled, this

blue colour usually appears so intensely

that the original yellow tint totally dis-

appears; in the thick walled cells, on the

contrary, especially those of wood, the

strong yellow colour is not altogether |. oa of cocos botryoph
overcome, and the colour assumes a dirty a, Peadliys Sesion veocns
green tint; lastly, in others no blue co- SA ee ee ee
lour is produced at all, and the membrane

offers such resistance, even to concentrated sulphuric acid, that
it either only swells up slightly or remains quite unaltered, only
becoming coloured deep brown ; as is the case particularly in ex-
ternal layers of epidermis-cells and the outermost layers of almost
all full-crown cells, especially those of wood. This outermost layer
may readily be taken for the primary membrane of the cell; but
as a rule it is composed of several super-imposed layers, and fre-
quently contains the outer ends of the pit canals (fig. 84), whence

26 ANATOMY AND PHYSIOLOGY OF

it is quite clear that in an anatomical sense it is not a well-defined
membrane, but that it is composed of the primary membrane,
and a few layers which belong to the secondary deposits, and
which have undergone the same chemical changes as the primary
membrane itself.

Besides the nitrogenous compounds and the colouring matters
which are diffused through many cells, especially those of the
wood, the membranes of a great number of cells also afford a series
of compounds devoid of nitrogen, which sometimes have a differ-
ent composition from cellulose, sometimes are isomerous with it.
Compounds of the first kind in which carbon, and, still more,
hydrogen, are contained in relatively greater quantity than in
cellulose, occur in the cell-membranes of fully developed wood, on
which account all the earlier elementary analyses of wood give a
false result, since the mixture of different compounds forming the
cells of the wood was taken for a simple combination (the so-
called woody fibre).

While it is beyond doubt that all the compounds differing from
cellulose in composition, form interstitial deposits in the cell-
membrane composed of cellulose, entering into it subsequently to
its first production, it is on the other hand doubtful whether the
compounds which are composed, like cellulose, of carbon and the
‘constituents of water, and which are either isomerous with cellu-
lgse, or differ from it perhaps only in containing a smaller amount
of water, are to be regarded in like manner as depositions in the
cellulose, or whether they replace cellulose and form the cell-
membrane itself, or at least some of the layers of it. Doubts in
reference to this point are raised, especially by the cells of many
of the lower plants, ¢.g., the cells of many Lichens, as of Cetraria
islandica, which are partially soluble in hot water, and yield a
substance similar to starch; also the cells of many Algee, as Sphe-
rococeus crispus, which yield a mucilage by boiling, and of which
Kiitzing (“Phycologia generalis”) assumed that they were com-
posed of a peculiar compound, named by him phytogelam. In none
of these cases can we state with any certainty whether, or what
share, cellulose takes in the formation of these membranes; and as
little whether or not inorganic compounds, which might modify
the characters of the cell-membrane by their action, are com-
' bined with it. We labour under the same uncertainty in regard
| to the differences which distinguish young cells from those in older
' conditions. Thus the membrane of the former swells up strongly
| in water, and is not coloured blue by iodine alone (but only by
iodine and sulphuric acid). We have not at present any definite
facts to enable us to express a decided opinion whether we are to
assume that the compound of which the young cell-membrane is
formed is essentially different from cellulose, and during the pro-
evessive development of the cell undergoes a chemical metamor-
phosis, a change of arrangement of its constituents or the like, or

THE VEGETABLE CELL. O7

that this compound is replaced by cellulose, or that both are to be
regarded as the same compound only distinguishable by slight
differences in their conditions of aggregation ; or that the differ-
ences are caused by the interstitial deposition of various foreign
compounds. The same occurs in reference to the substance of
those cells which are coloured blue with the same facility as
starch, by the action of a weak tincture of iodine, but differ from
starch by their behaviour to warm water, as is the case in the
horny albumen of many plants, e. g., of Cyclamen, in the cells of
the embryo of Schotia, &. (See “On the Blue Colouring of Ve-
getable Cell-membrane by Iodine,” in my “Vermischte Schriften,”
335.)

Observ. 1. The credié is due to Payen (“Memoires sur les developpe-
ments des vegetaux,’ 1844) of having demonstrated that the substance of
all cells, from the highest plants down to the Fungi, when purified from
foreign deposits, exhibits the same composition, and assumes the blue
colour of cellulose on treatment with iodine and sulphuric acid. Accord-
ing to his views the cellulose occurs in a tolerably pure condition in very
young cells, while the membranes of older cells are combined more or less
with foreign organic or inorganic compounds (which he called incrusting
substances), through the presence of which the physical and chemical pro-
perties of the cell-membrane undergo alterations. These incrusting sub-
stances may be more or less completely extracted by treating the cellulose
tissue with acids, ammonia, alcohol, ether, &. Thus, according to his
statement, nitrogenous substances and silica occur in the cuticle, pectate
and pectinate of lime and of the alkalies in the thick walled epidermal
cells of the Cactec, inuline in the cells of the Lichens and Alge, and in
the hard cells of wood capable of being polished three or four compounds,
designated by Payen lignose, lignone, lignine, and lignimose, substances
which are richer than cellulose in carbon and hydrogen.

Observ. 2. We owe to Mulder (“Physiological Chem.” ) very extensive
researches on the chemical conditions of the walls of the elementary
organs. He also, like Payen, arrived at the result, that the membrane of
all young organs consists of cellulose in almost a pure condition (the for-
mula of which he determined as C24, H42, O21) ; but in reference to the
alterations which the membranes undergo in the course of time, he pro-
pounded totally different views. He here starts from the fundamental
doctrine that a given layer of an elementary organ which is not coloured
blue by iodine and sulphuric acid, does not contain cellulose ; that there-
fore, when the same layer can be demonstrated to consist of cellulose in
the earliest periods of the growth of the elementary organ, the cellulose
must have been displaced by other compounds, or that if this origin from
a layer of cellulose cannot be demonstrated, it is a later formation, and
has been composed of other compounds from the first. In this way he
arrives at the conclusion, that the membrane of the elementary organs
increases in thickness in three ways :—1, By the deposition of younger
layers upon the inside of the membrane ; this occurs in the vessels and in
a doubtful manner in the thickened pith-cells of Hoya carnosa. 2, By
the deposition of layers upon the outside of the elementary organs, which
occurs generally in cells ; in.parenchymatous cells layers of the same kind

f

=

28 ANATOMY AND PHYSIOLOGY OF

alone are generally deposited ; in wood-cells, on the contrary, first an
outer coat is formed, and then subsequently intermediate layers of consi-
derable thickness are formed between this and the inner primary mem-
brane. 3, The new substances are deposited in the cell-wall of many
cells (in the horny albumen of Phytelephas, Jris, and the so-called collen-
chymatous cells), and therefore the wall does not exhibit lamellation.
The constitution of these different deposits is described as very varied.

| Proteine is shewn to be merely an infiltrated matter, taking no part in
| the formation of the cell-wall, and is wholly wanting, or only just trace-
_ able in very young cell-membranes; but it occurs in the intermediate
| substance of all old wood-cells, and most old pith-cells, but not in bark-

cells or collenchymatous cells. The following compounds are particularly
noticed as forming definite layers of the elementary organs. Intermediate
wood-substance (the formula of which is stated at C1o, Hse, O26), a com-
pound which is coloured yellow by iodine and sulphuric acid, swells up in
weak acid and dissolves in stronger ; it gradually displaces the cellulose
more or less perfectly in the secondary layer of vessels, forms the outer
layers of pith-cells and the intermediate of the wood-cells, m which it
becomes the more intimately combined with the cellulose the further the
layers lie toward the inside. Haternal wood-substance, which is coloured.
brown. by iodine and sulphuric acid, and does not dissolve in the latter ;
it is stated as probable that this is isomerous with the intermediate wood-
substance, but (as in the woody matter of the putamen of hard fruits) is
distinguished from it by containing whmin. It forms the outer layer of
wood-cells, scalariform ducts, and pitted vessels. Besides these more
generally distributed compounds, there occur other peculiar, less exten-
sively prevalent, compounds not yet fully characterized, one of which
forms the cuticle; another the cells of cork ; another the cells of the horny
albumen of Iris and Alstrameria. The following are regarded as incrust-
ing compounds, penetrating into the substance of the cell-wall: pectose in
the cells of the collenchyma, of the Apple, &c.; starch in Cetraria islan-
dica ; vegetable mucilage in Spheerococcus crispus ; and a peculiar sub-
stance isomerous with cellulose, in the cells of the albumen of Phytelephas.

My own investigations (“nvestigation of the question ‘ Does cellulose
form the basis of all vegetable membranes ??” —Botan. Zeit. 1847, 497) com-
pel me to declare most distinctly against the view of Mulder’s, that a
great proportion of the layers composing the membranes are from the
first composed of compounds different from cellulose ; and also against
his opinion as to the relative ages of the layers, deduced from these pro-
positions (which I have already discussed above under an anatomical point
of view). I found that the application of iodine and sulphuric acid, in
which Mulder places such unconditional trust, is a means in the highest
degree unsafe for deciding whether a membrane contains cellulose or not.
My researches shewed me that the influence of sulphuric acid was by no
means necessary for the production of the blue colour in membranes which
are not strongly incrusted, as in the parenchymatous cells of succulent
organs, but that iodine and water alone are suflicient ; while in full-grown
and hardened cells sometimes the primary membrane alone, sometimes
even a greater or smaller portion of the secondary layers had, through the
deposition of foreign substances, altogether lost the property of becoming
blue on the application of sulphuric acid and iodine, although they were

THE VEGETABLE CELL. 29

still composed of cellulose, and iodine alone would very readily produce a
blue colour in all their membranes after the infiltrated matters had been
removed. The means I employed to remove the infiltrated substances
were caustic potash and nitric acid. The first proved to be most effective
in the cells forming the surfaces of plants (such as epidermal cells, periderm
and cork); a maceration for twenty-four to forty-eight hours in strong so-
lution of potash, at common temperatures, caused iodine to produce a pure
blue colour in all these cells. The application of potash is not so effective
in the cells situated in the interior of the plant, but that of nitric acid
always answers the purpose completely, either when the preparation is left
to macerate for a length of time in dilute acid, or is boiled in acid of mo-
derate strength until the yellow colour which it assumes at first has dis-
appeared again. After this treatment, the whole of the layers of all
elementary organs are coloured a beautiful blue by iodme even when they
offer so great a resistance to the action of sulphuric acid before the treat-
ment with nitric, as is the case in the outer membrane of wood-cells and
of vessels, and in the brown cells at the circumference of the vascular
bundles in Ferns. After these experiments there cannot be any doubt,
that cellulose forms the basis of all the membranes of the higher plants,
that the greater or less resistance of many membranes to the combined
action of iodine and sulphuric acid, is caused by infiltrated foreign com-
pounds, and that the “substance” of cuticle, of cork, and the “outer and
middle wood-substance,” regarded by Mulder as peculiar compounds, are
combinations of cellulose with foreign infiltrated deposits. Of what nature
these deposits are, which interfere with the reaction of cellulose, future
researches of chemists must decide.

Observ. 3. Schleiden takes up quite a different point of view. (“On
Amyloid.” Beitrige, i. 168. “Some remarks on the substance of vege-
table membranes.” Beitrdge i. 172.) Without regarding that the cell-
walls are not composed of one chemical compound, but that they have
a series of substances deposited in them, possibly exerting an influence
upon their properties,—he considers the differences which are observed
in the cell-membranes as unconditional proofs of difference in the sub-
stances of which they are formed, and believes that the compounds dis-
tinguished by chemists, forming the series of hydrates of carbon, are
but a very sparing selection from the infinite multiplicity of compounds
belonging to this series, occurring in plants. According to his views, the
plant forms a fundamental substance, which remains the same in re-
ference to its elementary composition, but is capable of infinite modi-
fications by internal imperceptible changes, and also, in part by the in-
crease or diminution of chemically combined water: forming a series, the
adjoining members of which differ imperceptibly to us, sugar being the
lowest, and the substance of perfectly developed membrane the highest,
of the members, which become more and more insoluble in water from
below upward. Three compounds, in particular, of this series, forming
cell-membranes, are minutely characterized according to their behaviour
to iodine and water: 1, Cellulose, of which it is stated that it is not
coloured blue by iodine, when in a pure condition (“Grundz. der wiss.
Botanik,” 3rd. ed., i. 172), which is decidedly untrue. 2, Amyloid ;—
Schleiden used this name to signify the substance, announced by himself
and Vogel, composing the horny cells of the cotyledons of Schotia, Hy-

30 ANATOMY AND PHYSIOLOGY OF

mencea, Mucuna, and Tamarindus, which are readily coloured blue by
iodine. According to his account amyloid dissolves in boiling water, and
its compounds with iodine are dissolved in water with a golden yellow
colour. The latter is decidedly incorrect, and in regard to the former,
Schleiden himself says (“Beittréige,” i. 167), only the intermediate layers
were dissolved even after twelve hours boiling, and all the cellulose tissue
remained. 3, Vegetable Jelly ;—under this name Schleiden comprised a
series of compounds, which chemists mention under different names (Bas-
sorin, Cerasin, Pectin, Gelin, &e.), but which he united on account of
their property of swelling up strongly in water and not becoming coloured
by iodine. He ascribed to this substance the property of gradually be-
coming diffused in cold water, and believed many vegetable cells to be
composed of this substance, transitions from it existing on the one hand
(through the cells of the Fucacese) into cellulose, and on the other (by
many kinds of horny albumen) into amyloid. Excepting the statements
that cellulose is not coloured by iodine, and that there exist cells soluble
in water, there is no doubt of the correctness of the anatomical founda-
tions on which this theory rests. But on the other hand, there is just as
little doubt that the whole of this representation of the infinite multipli-
city of neutral hydrates of carbon and the distinction between them ac-
cording to their greater or less expansion in water, and more or less
facility with which they are coloured by iodine, could only be considered
as established, when it was proved that the substance of vegetable cells
possessed this property in its pure condition, and that these differences
were not caused by foreign deposits. Since not only is this proof wanting,
but, on the contrary, the most definite evidence exists that the chemical
and physical properties of vegetable membranes can be modified in the
greatest degree by infiltrated matters, Schleiden’s view is devoid of any
solid foundation.

D. CELLS IN THEIR RECIPROCAL, CONNEXION. ©

Leaving out of view the lowest plants, and the spores and pol-
len-grains of the more highly organized, cells do not occur isolated,
but grown together in great numbers in connected masses; in
this manner they form the so-called cellular tissue, contextus
cellulosus (parenchyma or prosenchyma, according as it is com-
posed of parenchymatous or prosenchymatous cells).

From the structure of the cell, as a closed vesicle formed of a
special membrane, it follows that in cellular tissue the partitions
between any two cell-cavities must necessarily be composed of a
double membrane, and this may be readily observed in reference
to the secondary layers, in all thick walled cells, by means of the
microscope, for it is clearly seen, that the individual layers of the
membranes surround the cavities of the cells concentrically, and
that the secondary layers of the several cells are separated from
each other by the primary membrane.

Observ. Tt is by no means so simple an affair as it seems at first sight
to determine the limit between two cells. Formerly, when observers
were restricted to weaker and less perfect magnifying instruments, the sur-

THE VEGETABLE CELL. ol

face of the cross section of the primary membrane appeared as so narrow
a line, that it was taken for the boundary line between two neighbouring
cells, and was drawn as such. Subsequently, when the knowledge of
cellulose structure had progressed further, the primary membrane was
distinguished from the secondary layers, and the outermost layer of cell-
membrane was seen under stronger microscopes to have a clearly visible
breadth (or thickness), the idea remained of an easily distinguishable
boundary line between the two coherent cells, and such a line was even
figured. This, as Hartig correctly observed, was untrue, for our micro-
scopes do not shew any boundary line between the two coherent primary
membranes (see figs. 21, 22, 25, 32, 44). When Hartig drew from this
the general conclusion that no limit exists, and that the outer membrane
of the two cells is common to both, his induction was too hasty. The
impossibility of seeing a line of demarcation with our microscopes, war-
rants, @ priori, nothing more than the conjecture that our present instru-
ments are not yet sufficiently perfect for the purpose. It is self-evident
under these circumstances that nothing has been accurately made out as
to the manner in which cells are connected.

The cells cohering together may be separated from each other;
in very succulent tissues, as in the parenchyma of many juicy
fruits, a slight pressure suffices for this; in somewhat firmer tis-
sues the connexion of the cells may often be so loosened by boil-
ing in water or by freezing, as to become easily separable ; while
in very solid tissues a long maceration in water or a short boiling
in nitric acid is necessary. It might be imagined that the double
nature of the outer membrane could be readily demonstrated b
this separation of the cells, but wrongly, for I found that the
outer membrane, when distinctly perceptible, was not split into
two layers in such cases, but torn into pieces, some adhering to
one and some to the other cell, so that the separated cells were
composed chiefly of secondary layers.*

It has been remarked already, in the description of the form of
cells, that the flat faces of cells meet at sharp angles in compara-
tively few cases, since the corners and edges are generally rounded
off. It follows necessarily from this condition, that the cells are
not, for the most part, coherent together by their whole surfaces,
but leave empty spaces between them, which run along the edges
of the cells in the form of triangular canals having no special
walls of their own, opening into each other at the corners of the
cells, and so forming a net-work of narrow and wide tubes branch-
ing throughout the whole plant, to which the name of imtercellu-
lar passages has been applied (see figs. 6, 7). In living plants they
are, with few exceptions, filled with air.

* Schultz has lately made known a process for isolating the conjoined
cells even of woody tissues. It consists in boiling them for a short time
with chlorate of potash in nitric acid. It is not clear, however, that this
does not dissolve the outer membranes.—A. H.

oo ANATOMY AND PHYSIOLOGY OF

Intercellular passages occur mostly between parenchymatous
cells; they are frequently absent from prosenchyma, or when pre-
sent, are, at least, very narrow. They are closed in most places at
the surface of the plant, since the parenchymatous cells which form
the outermost layer of the plant are, in general, and in all parts
growing under ground or in water without exception, accurately
in contact at their angles ; on the other hand, on most organs ex-
posed to the air, especially on the lower sides of leaves, there
occur little orifices bounded by crescent-shaped, curved. cells, sto-

mates or stomata (fig. 35), which allow
Fig. 35. a free communication between the air

yf contained in the intercellular passages
= = and the atmosphere.
pe VS p | The more regularly polyhedral the

( \ cells are, the more do the intercellular
passages take the form of regular, nar-
row canals (see fig. 7); on the other
hand, the more globular the shape of
the cells (fig. 6), and in a still higher
degree, the more an unequal growth
has caused them to approach the form
of the stellate cell (fig. 10), the more
do the intercellular passages take the
form of irregular cavities, and the more
spongy becomes the tissue of the organ
formed of such cells, since the space

oes occupied by the intercellular passages
bees! ek ea Re ees then becomes more equal to, or in ex-

treme cases, many times surpasses, that
filled by the cells. The lower side of leaves and corollas are
formed of such tissue, moderately spongy, the pith of Juncus
effusus gives a Very: highly developed example.

In other cases the intercellular passages lying between regular
polyhedral cells become expanded at particular points into larger
cavities, or into long canals, which latter are frequently interrupted
at certain distances by partitions composed of stellate cells. This
ig the case in the stem and in the leaf-stalk of many water- and
marsh-plants, in which the wide, regular air-canals are often sepa-
rated from each only by a single layer of parenchymatous cells ;
there also exists a roundish air-cavity (breathing-cavity, Ath-
mungshdhle) beneath each stomate. Canals and cavities of this
kind serve in other cases as reservoirs for peculiar fluids secreted
by the neighbouring cells, ¢.¢,, for balsams in the Coniferze, for
etherial oils in the Umbelliferee, Aurantiacez, &ec., for gum in the
Limes, Cycade, and for milk-sap in Rhus.

In many cases the spaces between the cells are filled up with a
solid matter, the imtercellular substance, which is secreted by the
cells upon the outer surface, and sometimes only imperfectly fills

THE VEGETABLE CELL. 30

the intercellular passages, but usually forms a dense mass in it
and quite obliterates its cavity. This occurs in remarkable quan-

tity in the tissue of many Alove, especially of the Fucoideve, the

Nostochinez, in the cortical

layer of many Lichens, in

the Albumen of many Legu-

minose, @.g., Sophora japo-

nica (fig. 36), Gleditschia, &e.

It is found in smaller quan-

tity, and therefore less readily

perceptible, in the intercellu-

lar passages of wood, ¢. g., of

Pinus (fig. 22) and Buaus, as

well as in the intercellular

substance of bark. The mass

composing the intercellular

substance usually resembles

so much the substance of the

cell-walls between which it

lies, that the application of

re-agents, as of iodine and _Transverse section through the albumen of So-
2 i phora japonica ; a, intercellular substance ; b, cavity

sulphuric acid, does not af- of the'cells.

ford any certain means of .

accurately distinguishing it from cell-membrane ; in other cases

the boundary line between them is very sharply defined.

An analogous secreted layer, appearing in the form of a mem-
brane, occurs upon the surface of freely exposed cells ; it possesses,
like the outermost membrane of wood-cells, the property of resist-
ing obstinately the solvent power of sulphuric acid. To this be-
long the outer membrane of spores and pollen-grains and the cuticle
(fig. 37, a), which invests the whole '

of the surface exposed to the air
of the higher plants, in the form es
of a connected membrane. Baa

Ig. 37.

Observ. When I propounded the
theory of the intercellular substance
(“Illustrations and Defence of my
View of the Structure of Vegetable
Substance,” 1836), this appeared to me
oY gobi ea far ger a ae a Cells of the epidermis of the leaf of Helle-
the vegetable organism, than it proved borus foetidus. a, cuticle.
to have subsequently on more accu-
rate investigation of this substance itself. and more minute research
into the development of cells. I did not perceive that the intercellular
substance is a product of the cell, and thought I had discovered in it an
universally distributed mass, in which the cells are imbedded, and which,
in many cases, exists before the formation of the cells. he real condition
is in most cases decidedly the reverse ; but 1t is not yet, however, clearly

D

34 ANATOMY AND PHYSIOLOGY OF

made out whether or not, in certain cases, for instance in the albumen.
of Schizolobium excelswm (see Schleiden on “ Albwmen” in the “Nova
act. Natur. Curios.” xix. p. 11, pl. xliii, fig. 55), cells and intercellular
substance originate together; but nothing can be decidedly determined
about this, since we are altogether without observations on the develop-
ment.

In very many cases it is extraordinarily difficult to distinguish the in-
tercellular substance from the cell-wall. In regard to this, my opinions
differ in many cases from those of many other ob-
servers ; for instance, of Schleiden, especially im re-
lation to the structure of the cells which swell up
in a jelly-like manner in water (the so-called collen-
chyma-cells), which occur in the outer layer of the
rind in many plants; for example, in Cucurbita
Pepo, and Beta vulgaris (fig. 38), m which, accord-
ing to my view, the parts swelling up (a) belong
to the cell-membrane, and are formed of second-
ary layers deposited in the angles of the cells ;
while, according to the opinion I formerly ex-
pressed, still defended by Schleiden, the cells possess
walls of uniform thickness, and the laminated mass
lying between their angles is to be regarded as in-
tercellular substance. In such difficult cases it is
best to allow the cells to swell up in nitric acid, to
render the stratification of their membrane more dis-
tinct, and thus to make out the position of the primary membrane (fig. 39).

Unger (“ Botan. Zeitung,” 1847, 289) has recently sought to demon-
strate that the origin of the intercellular substance and of the cells is
simultaneous. The reasons advanced by him do
not seem to me convincing. In the present state
of our knowledge, however, we can say very little
about this ; the whole theory of the mtercellular
substance requires a thoroughly new investigation.

The membrane secreted upon the surface of cells
exhibits most remarkable conditions, since no inter-
nal organization or composition from different layers
can be detected in it, while it is yet very frequently
clothed in an extremely complicated manner with
reticulated projecting ridges, straight or waving

Collenchyma-cells from the
stem of Beta vulgaris. In
the angles of the cells the
substance of their membrane
(a) is very hygroscopic, and
swells up gelatinously in
water.

Pig. 39,

The point of union of four

cells of Beta swollen up in
hydrochloric acid. It shews
the uniform dense tertiary
layer (b); the gelatinous
secondary layers (@); and
the primary membrane (c).

jacent cells.
these membranes are composed ; cellulose is not found in them.
The structure and origin of the cuticle, and the epidermis-cells lying

beneath it, have been the subjects of manifold discussions.

lines, or granular or spiny projections, as is seen in
the most varied and elegant manner on many
spores and pollen-grains. Linear projections also
oceur frequently upon the cuticle, and these are by
no means arranged in. correspondence with the sub-

Té is not at present known of what chemical compound

When an

epidermis, especially one from the upper side of a leathery leaf, is sliced
transversely, the walls of its cells turned outwards are seen to be much
thicker than the rest. Iodine and sulphuric acid either colour the whole
of this outer wall dark yellow, and sulphuric acid does not dissolve it, or,

THE VEGETABLE CELL.

the outer wall exhibits these properties down to a certain depth, so that
a layer (fig. 40, a) is thus formed, which is
most strikingly distinct from the subja-
cent cells, and when the latter have been “ ee
dissolved in sulphuric acid, remains behind CSN ASM
as a continuous and apparently homogene- ~ a —
ous membrane. Since Ad. Brongniart
(“ Ann. des Se. Nat. Sér.,” § i, 65) had dis-
covered that a continuous membrane, not Ciele OF thie-ep aettine of ta:
composed of cells, called by him cuticula, ee ee

. 4 ay i eis - the portion of their wails ac
might be separated by maceration from yellow colour with iodine.
the outer surface of the epidermis, it ap-
peared natural to suppose that the layer just spoken of, which is fre-
quently very thick andis coloured brown by iodine and sulphuric acid,
was this cuticula, and to ascribe its origin to a secretion upon the outside
of the epidermis-cells, a process of which Schleiden even gave a detailed
description (“Grundz. der-wiss. Bot.,” 1st ed. i, 288). This view, however,
proposed -by Treviranus, and defended by Unger, Harting, Mulder, and
others, is in great part wrong. The so-called cuticle consists, with the
exception of a layer extremely thin in most
plants (fig. 41, a), of the thickened walls of
the cells, which are infiltrated with a sub- a a
stance coloured brown by iodine, to which -
they owe their power of resisting the action ==

?

of sulphuric acid. When this substance is Cae (

Fig. 41.

EE Ep

S ZN re
. Fy SSS Se
removed by caustic potash, not only is the “Sy i y=
composition out of cell-membranes evident, The epidermis of the upper side

n 4 eee Pia Ae “
since the separate layers of these become ithe leaf of Hoya carnosa treated
© alkali. a, the cuticle

visible, but iodine now very readily produces a _ separatin: b, the swollen, lami-

bine onlour (“Lot Zacung, 1947,092) This jac. ee

composition of the so-called cuticle, of cell-

membranes, is seen beyond all doubt in the epidermis of an old stem of

Viscum album (fig. 42) ; the epidermis-cells consist here of two or three

generations enclosed one within

another, of which ali the thick-

ened walls on the outer side

have become blended together

into a membrane composing the

cuticle (H. v. Mohl, “On the

Epidermis of Viscum album,”

—Bot. Zeitung, 1849). T call

these layers belonging to the

epidermal cells the cuticular

layers of the epidermis, to dis-

tinguish them from the mass

secreted on the outside of the

cells, the true cuticle, which is

soluble in caustic potash, in

most cases forms but a very

thin coating over the epidermal Epidermis of an old stem of Viseum album.

cells, and only rarely, as in the

shoots of Hphedra, and the upper surface of the leaves of Cycas, forms
Dp 2

36 ANATOMY AND PHYSIOLOGY OF

a layer of considerable thickness, and in which no cellular has yet been
shewn to exist.

E. CONTENTS OF CELLS.

In the present state of our knowledge it is an impossibility to
give even a tolerably complete description of the contents of cells,
since of the large number of organic compounds produced by the
vegetative processes, almost all of which occur in the cells, only a
very small number can be demonstrated at present in the plant
itself by means of the microscope, since most of them occur in
solution in the cell-sap and in too small quantity for them to be
rendered visible by re-agents. I must, therefore, confine myself to
the mention of the organized productions found in cells, and the
universally diffused substances.

a. Primordial Utricle, Protoplasm and Nucleus.

In all young cells, whatever their subsequent contents may be,
whether they persist in the stage of cells or become changed into
vascular utricles, a series of formations are met with, which dis-
appear again more or less perfectly in the subsequent periods of
life, and which stand in the closest relation to the origin and
growth of the young cell, but only in particular cases in relation
to their later functions.

If a tissue composed of young cells be left some time in alcohol,
or treated with nitric or muriatic acid, avery thin, finely granular
membrane becomes detached from the inside of the wall of the
cells, in the form of a closed vesicle, which becomes more or less
contracted, and consequently removes all the contents of the
cell, which are enclosed in this vesicle, from the wall of the cell.
Reasons hereafter to be discussed have led me to call this inner

cell (fig. 48, a) the primordial

Ea utricle(prvmordialschlauch)

(H. v. Mohl, “ Remarks on

the Structure of the Vege-

table Cell,’—Bot. Zeitung,

1844, 273. Transl. im Tay-

lor’s Scientific Memovrs, vol.

iv. p. 91). lodine colours it

yellow, and it is therefore

probably always nitrogen-

ous. According to Mulder,

proteine may be detected in

it in many, but not all, cases,

by nitric acid. Cellulose

cannot be found in it, and

Cell of the leaf of Jungermannia Taylori. a, the the compound of which it is
primordial utricle separated by the action of iodine. comp ose d is as y et unkn. Own.

The primordial utricle disappears again with the thickening of

THE VEGETABLE CELL. 37

the walls of the vessels, the cells of the wood, of the pith, of the
inner part of the petiole, and of thick leaves. It usually adheres
firmly to the cell-wall, and can be discovered even at first in the
form of a thin granular coat, coloured yellow by iodine, when the
cell-wall is dissolved in Sulphuric acid ; in particular cases it ap~
peared to me not to be so firmly connected, but to be dissolved
and to assume before it vanished the form of an irregular net of
fibre-like streaks. On the other hand, the primordial utricle re-
tains its complete integrity throughout the whole life of those
cells which contain chlorophyll, thus especially in the cells of
leaves, and in those of the fleshy rind of the Cacteze, Huphorbie,
&ec., and in like manner in the cells of many Cellular plants, par-
ticularly of the Algee.

Observ. Tt was natural enough that the primordial utricle should have
been seen by others before I called attention to its existence as an univer-
sally prevailing structure; in particular, Kiitzing (Linnwa, 1841, 546,
“ Phycologia generalis,” 38) had discovered it in the Algz, and described it
as a special coat of the cell under the name of the Amylid-cell. He applied
this unsuitable name under the idea that its substance was changed into
starch by the action of potash, which is not the case. Karsten had de-
scribed the same in his “Déssertatio de cella Vitali,” but attributed import
to it quite different from that I have, since he considered it to be a secon-
dary cell. Niageli (“Zeitschrift f; wiss. Botan.” i. 96) had detected it in the
Alge, but taken it not for a membrane, but a layer of mucilage,—a view
in which Schleiden appears to participate. I must declare against this
opinion in toto. No fixed limit can, of course, be indicated between a soft
membrane and a compact layer of mucilage, but a layer
from which (as will be described more minutely further
on) folds grow out and cause constriction of the contents
of the cell, certainly must be regarded as a membrane,
and not a layer of fluid ‘mucilage.

In the centre of the young cell (fig. 44), with rare —

exceptions, lies the so-called nucleus cellule of Rob.

Brown (“Zellen-kern ;” “Cytoblast” of Schleiden) ;

the origin of this will be treated more minutely here-

after in the description of the origin of cells ; it is

usually of very considerable size in proportion to

the magnitude of the young cell, so that in parti-

cular cases, é. g., in the cells of jointed hairs, it almost

fills up the cavity. The remainder of the cell is

more or less densely filled with an opake, viscid

fluid of a white colour, having granules intermin- :
| gled in it, which fluid I call protoplasm ( 3 On the Cell from the stem
| | Movement of Sap in the Interior of the Cell,’ —Bot. ae
|| Zeitung, 1846, 73). This fluid is coloured yellow by

| iodine, coagulated by alcohol and acids, and contains albumen in
' abundance, whence young organs are always very rich in nitrogen,

38 ANATOMY AND PHYSIOLOGY OF
As the cell increases in size, its membrane grows in much greater
proportion than the nucleus, which certainly frequently enlarges
for a certain time, but becomes smaller in proportion to the cell.

| During the growth of the cell irregularly scattered cavities are

jformed in the protoplasm ; these are originally isolated, and very

i frequently present a most deceptive resemblance to cavities of

delicate-walled cells, subsequently, however, they become blended
together in many directions ; the protoplasm is then accumulated
at one side, in the vicinity of the nucleus; on the other side it
coats the inside of the primordial utricle, and these two collections
are connected together by thread-like processes which are some-
times simple and sometimes branched, so that the nucleus appears
suspended, as in a spider’s web, in the centre of the cell* An
internal movement in the protoplasm now begins to be visible.
Originally no definite arrangement can be perceived in it ; but
the more the protoplasm changes from the uniform mass which
it originally formed, into the condition of threads, the more dis-
tinctly it may be seen that each of these threads represents a
thinner or thicker stream, which in one thread flows from the
nucleus to the periphery, turns round there, and flows back again
in another thread. The thickness, the position, and the number
of these threads are subject to constant change, which shews,
beyond a doubt, that the currents move freely through the watery
cell-sap, and are not enclosed in membranous canals. In most
cases the nucleus does not appear to take any part in this move-
ment ; but the motion may easily be overlooked on account of its
slowness, since I found in Tradescantia virginica, in which I saw
the nucleus move slowly up and down, that this only passed over

.. the distance of 1-45,000th of a line in a second, which is naturally
much too little to allow of the movement being seen directly,
even by the application of the strongest magnifying powers. The
nucleus retains its central position In many cases even when the
cell is fully developed, e.g., in Zygnema, but it mostly becomes
gradually withdrawn towards one side of the wall of the cell, where
it becomes attached by its viscid investment to the primordial
utricle, but always forms the centre of the currents of sap. The
circulation of the protoplasm is very slow; I determined it in the
hairs of the filaments of Tradescantia at an average of 1-500th of
a line per second, in the stinging hairs of Urtica baccifera 1-750th,
in the hairs of Cucurbita Pepo at 1-1857th, &. (“ Bot. Zevtung.”
1846, 92.)

In most cells this phenomenon is transitory, for not only is the
nucleus itself dissolved in time in the majority of cases, but the
protoplasm also becomes more and more diminished in quantity,
or at least frequently appears motionless, as appears in all proba-

* PL. 1, fig. 7. The end cell of a hair of the filament of Tradescantia
Setlowe.

THE VEGETABLE CELL. 39

bility to be the case in the cells of many succulent fruits, in which
the nucleus frequently remains perfect up to the time of the ma-
turation of the fruit. In one series of cases, however, the circu-
lation is persistent in the full-grown cell, e. g., in the stinging hairs
of nettles and Loase, in the hairs of Cucurbitaceous plants, in the
hairs of the filaments of Z’radescantia, in the hairs of the corolla
of Campanula Mediwm, in the cells of the leaves of Sagittaria
sagittifolia, Stratiotes aloides. In some plants the protoplasm is
not distributed in isolated reticularly arranged currents, but flows
along the cell-wall ina broad stream, returning back upon itself in
a circular direction at one side of the top of the cell, and flowing
down upon the other side, the nucleus following the current. This
form of the circulation is displayed very beautifully in the cells of
the leaves of Vallisneria spiralis, and in the cells of Chara, the
inside of which is clothed with spirally arranged rows of chloro-
phyll granules, which the current accurately follows.

Observ. 1. The wonderful phenomenon of the movement of the proto-
plasm is usually designated by the most unsuitable name of “rotation of
the cell-sap.” Although described by Corti in 1774, the phenomenon
was altogether forgotten till discovered a second time by Treviranus in
Chara, in 1807. For a long time it was supposed to be a peculiarity
- belonging to a few water plants (Chara, I, ydrocharis, Vallisneria, Cau-
linia), until the researches of recent times shewed that it was an univer-
sal phenomenon. ‘The cause of the motion is altogether unknown ; the
explanation of Amici, that in Chara the rows of chlorophyll granules which
clothe the walls of the cells, and which the current of sap follows, exer-
cise a galvanic action upon the sap, and thus give rise to the motion, can-
not be considered applicable, since these granules are absent in all other
plants and even in the roots of Chara. The description of the pheno-
menon in question, by Schultz, furnishes a pattern of imperfect observa-
tion and unfortunate conclusions ; he regards the currents of protoplasm
as composed of milk-sap, flowing in a branched vascular system, having
its origin in the vessels of the milk-sap, and penetrating the walls of the
cells (“Die Cyclosis des Lebensaftes im der Phlanze,” 293).

Observ. 2. According to Schleiden’s statement (“Grundz,” 1. 211, pl. iF
fig. 6), it sometimes happens that a secondary cell-membrane becomes
deposited over the nucleus as it lies upon the wall of the cell, so that it is
enclosed in the substance of the cell-znembrane and protected from fur-
ther change. This account is altogether incorrect. ‘The nucleus, like all
the rest. of the contents of the cell, lies in the cavity of the primordial
utricle, and the cell-membranes are formed over the outside of the latter.
The conditions which determine the early solution of the nucleus or its
persistence in the full-grown cell, are altogether unknown. It vanishes
very soon in vascular utricles and in wood-cells ; it has likewise very often
disappeared from full-grown parenchyma-cells, especially in those of the
middle layers of the stem, while it is very frequently found quite perfect
in spores, pollen-grains, in the cells of jointed hairs, in the cells of berries,
and in the boundary cells of stomates ; the cellular tissue of many Or-
chidese and Commelynacecze is remarkable for the long retention of the
nucleus.

AQ ANATOMY AND PHYSIOLOGY OF

Observ. 3. It has already been remarked that the cavities in the pro-
topiasm, filled with watery cell-sap, sometimes deceptively resemble cells.
This is the case in a much less degree as long as the protoplasm is only
hollowed into distinct isolated cavities, but the similarity becomes very
great when the hollows have so increased in number or size, that the layers
of protoplasm between them have assumed the form of thin partitions.
In this case the cavities acquire the shape of polyhedral parenchymatous
cells ; and those lying on the surface of the mass of protoplasm become
rounded off on their free sides, as cells would in such a case ; in short, the
resemblance to a delicate-walled cellular tissue could not be greater. Yet
if we reflect that the protoplasm is a viscid fluid, which, as its delicate
currents shew most distinctly, does not mix with the watery cell-sap,
this appearance becomes comprehensible enough ; the protoplasm bears
the same relation to the cell-sap as a frothing fluid does to the air con-
tained in its bubbles. The unceasing flow and continued transformation
of the mass of the protoplasm, furnish most distinct proof that we have
to do with a fluid, and not with an organized structure. We must keep
in view this condition of the protoplasm of the young cells, if we would
avoid being deceived by the forms which it frequently presents in full-
grown cells, especially in those of succulent fruits, ¢. g., of Grapes. In
these it forms not only, in part, a connected frothing mass, but a portion
of it occurs in isolated globular masses, which usually contain in their
interior one or more cavities filled with cell-sap, and consequently possess
the form of vesicles, These are met with in every gradation of size, from
scarcely perceptible vesicles to bodies like cells, some 1-100th of an inch
in diameter. No more movement in the substance of the protoplasm can
be detected in these cases; on the contrary, the walls of these vesicles
exhibit a tolerable degree of firmness, so that the comparison of them
with cell-like structures is not at all far-fetched. Nevertheless, such a com-
parison seems to me out of place ; since none of our means,—for instance,
application of the compressor, or treatment of iodine,—will enable us to
discover on these vesicles a membrane which would form a contrast with
the contents. Under these circumstances, I can only regard as a mistake
Karsten’s view (“Creation,” Die Urzeugung.—Bot. Zeitung, 1848, 457 ;
“Contributions to the Knowledge of Cell-life.” — Bot. Zeit. 1848, 361),
according to which these utricles are the rudiments of cells.

b. Cell-sap.

In full-grown cells the protoplasm usually forms but a very
subordinate part, as to mass, of the contents of the cell; while the
watery cell-sap, which at first appeared only in isolated cavities,
formed by degrees in the protoplasm, fills the whole cavity of the
cell The quantity of it is subject to variation, according as the
plant has absorbed or evaporated more water; the decrease, how-
ever, cannot descend below a certain limit in the cells of most
ongepe of the higher plants, without destroying the life of the
cell.

Although the cell-sap always contains in solution a series of
organic and inorganic compounds, as a general rule it appears to
the eye like pure water, since it is but rarely that colouring mat-

THE VEGETABLE CELL. 4]

ters (usually red or blue) are dissolved in it; and still more
rarely is the quantity of the uncoloured substances, such as gum,
dissolved in it, so great as to increase in a striking manner its
power of refracting light.

In many, yet comparatively rare, cases, the cell-sap of particular
cells becomes wholly displaced by compounds which the cell itself
prepares, ¢. g., etherial oils.

Observ. Among the organs of the higher plants, ripe seeds alone bear
to be perfectly dried without being killed ; the older wood of trees may
also lose a great quantity of its sap without death ; the limit to which this
is possible is as yet unknown. The rest of the organs, particularly the
leaves, do not bear any considerable loss of water. It is different in many
lower plants, especially the Mosses, Lichens, and many Alge, e. g., in
WVostoc, which may be completely dried up without injury.

c Granular structures.

In the majority of parenchymatous cells, organic structures—
usually of granular form—are met with, at all events at certain
periods of the life, swimming in the cell-sap or slightly adherent
to the walls. Two of these, the chlorophyll granules and starch
are very generally diffused.

Chlorophyll (leaf-green), on the presence of which Fig, 45.
depends the green colour of plants, never occurs
dissolved in the sap, but always in the form of a
softish mass of definite or indefinite shape ; many
phytotomists have asserted the existence of a green-
coloured cell-sap, but I have never been able to
find it,

Amorphous chlorophyll forming patches or threads
which adheres to the éell-wall and the granules con-
tained in the cell, is of comparatively rare occur-
rence, yet it occurs here and there in the Phane-
rogamia, in the same cells with the chlorophyll
granules. Usually chlorophyll possesses a sharply
defined form. In certain Algze it presents itself in
the form of flat bands, in Conferva zonata, Dra-
parnaldia plumosa, &e., in each cell as a trans-
verse annular band; in Zygnema (fig. 45), in the
form of a spirally wound band; in Mougeotia, in
the form of a flat or curved plate lying in the in-
terior of the cell, &c. In the great majority of
plants, however (see fig. 10), it possesses the form
of globules, which sometimes lie upon the wall of Pei sinte
the cell (where they are usually irregularly scat-
tered, but in Chara arranged in rows), sometimes swim in the
cell-sap, and sometimes surround the nucleus,

But a very small portion both of the band-shaped masses in

i. ieee debater" ath. eeniiiie te oo i

oe

a See tieeay y

492, ANATOMY AND PHYSIOLOGY OF

Zygnema, &e., and of the chlorophyll globules consists of the green
colouring matter; so that in pieces of plants from which the
colour has been extracted by alcohol, they are found little altered
in size, as softish masses which are coloured yellow by iodine,
therefore contain nitrogen. Whether this is simply albumen, as
Treviranus states, remains to be proved; but it is probable that it
is a proteine compound.

Even in the matter extracted by ether, the true green colouring
substance forms but an extremely small portion, according to
Mulder’s researches (“ Physiological Chemistry,” 275), since the
great mass of that which is soluble in ether consists of wax. The
chemical composition of chlorophyll is not yet made out with cer-
tainty ; Mulder’s analysis gave Cis Hig Nz O3, but requires repeti-
tion. From his researches it would appear that chlorophyll is
allied to the indigo-like bodies, and Mulder considers it probable
that uncoloured chlorophyll exists in all parts of the plant,
capable of conversion into green by free oxygen ; a conjecture,
however, against which speaks the circumstance that neither the
expressed sap, nor any tissue whatever of plants, acquires a green
colour by exposure to the influence of the air.

Starch granules are very frequently enclosed in the chlorophyll
granules. (See “On the Anatomical Condition of Chlorophyll,”
in my “ Vermischte Schrift.”) and not only in the band-shaped
strips of Zygnema, but in an extraordinary number of cases in
the chlorophyll granules of the most varied plants, and especially
distinctly in those of Chara. Sometimes only one starch granule
exists in the chlorophyll grain, sometimes several, but usually not
more than three or four; in Anthoceros alone I found from 50 to
100 starch granules in each of them. These starch granules are
usually of very small size ; the longest I determined at 1-300th of
a line, the smallest, acquiring a distinct blue colour with iodine,
1-2000th of a line, and it still remains uncertain whether or not
still smaller granules, which occur in many cases in chlorophyll,
consist also of starch. The history of the development of chloro-
phyll is still involved in obscurity. So far as I have traced the
matter, it stands in the closest connexion with protoplasm at its
first appearance in uncoloured organs which have been developed
in the dark, when the formation of chlorophyll is brought about
in these by the influence of light ; for on the first appearance of
the green colour, isolated portions of the protoplasm are seen to
assume a greenish tint, exhibiting the form of granular patches of
mucilage having no definite outline. Subsequently, the starch
granules, where such occur in the cells, ¢ ¢., in the potato, or any
young leaves, become clothed by a more or less thick coat of
chlorophyll presenting a distinct boundary line; while in other
cells chlorophyll granules are met with which contain no starch.
Tn other cases in which the very young organs contain no starch,
e.g. in the vegetating points of Conferva glomerata, granules of

THE VEGETABLE CELL. 43

it appear at a later period in the perfect chlorophyll globules, and
increase in size with the age of the plant. Thus it seems to me
that starch does not stand in any causal and necessary connexion
with chlorophyll, but that the proteine substance combined with
chlorophyll sometimes assumes the definite form of globules,
bands, &¢., and sometimes, when starch granules are present, be-
comes deposited on these as upon a nucleus.

Observ. The relation of chlorophyll to starch is viewed in an essen-
tially different way by Mulder, who rests upon my description of the
former. He assumes that the chlorophyll granules are always produced
from starch granules, since the latter become partly or wholly converted
into the wax connected with the green colouring matter, and in so doing
either assume the form of globules or become blended together, and pro-
duce amorphous chlorophyll. This transformation of starch into “wax
must be accompanied by an abundant evolution of oxygen gas; and
Mulder therefore believes that plants do not exhale this gas because they
are green, but while they are becoming green. I cannot accept this
theory on account of anatomical reasons, for in many young organs we
find chlorophyll but not starch, which should precede it, and in the Con-
Jerve particularly, in which the chlorophyll occurs in the form of bands
and plates, as in Zygnema, &c., these structures never consist of a sub-
stance having any resemblance to starch, but, on the contrary, the starch
granules occurring in this chlorophyll increases in size with the age of the
plant.

Ooserv. 2. I have described the chlorophyll granules as a softish, homo-
geneous substance, and not as utricular structures, such as they were
formerly stated to be by Sprengel, Meyen, Agardh, Turpin, and others,
for I never could succeed in discovering upon them an enveloping mem-
brane distinct from the contents. Their utricular nature has, however,
been defended in recent times by Nageli. (“Zettschr. f. wiss. Botan.”
ii. 110); according to his statements, a whitish membrane and green
contents may be clearly distinguished in the large chlorophyll granules of
the Alge, Char, and Mosses. Also Géppert and Cohn (“Bot. Zeit.”
1849, 665) say that in Witella they saw the chlorophyll granules ex-
pand by absorption of water into vesicles composed of a thin translucent
membrane, which finally burst. I am not in a position at the present
moment to test these statements respecting the chlorophyll granules of
Niieita; but I have formerly frequently examined them and detected the
occurrence of starch granules in the chlorophyll, but could never find a
membrane upon the latter. Nigeli believes, moreover, not only that he
has seen a membrane in many cases, but that he has found proof of a
complete analogy of these vesicles, with cells, in the phenomena of their
vegetation. In this he is not warranted by a single fact ; for that the
chlorophyll granules may grow, and during growth alter in form, is no
proof at all of the cellular nature, any more than is the circumstance that
their number may be multiplied by division as in Witella. Division
might occur in globules devoid of a membrane ; but that it depends on
the formation of secondary vesicles inside the chlorophyll vesicles, is an
hypothesis devoid of all foundation. - ‘

Observ. 3. We know very little as yet of the anatomical conditions of

AA ANATOMY AND PHYSIOLOGY OF

the other colouring matters of plants. The reds and blues are usually
dissolved in the cell-sap ; in particular the red colouring matter of leaves,
which acquire this colour in autumn, that of most flowers and red fruits ;
and in like manner the blue colouring matter of most blue flowers. Only
in very rare cases do we find the red and blue colouring matter of flower
in the form of globules, ¢. g., the red of Salvia splendens and the blue of
Strelitzia reginw. Whether the pigment is here as in chlorophyll con-
nected with a foreign matter forming the globules, or itself alone consti-
tutes these is unknown. ‘The yellow colour of leaves which are bleached
in autumn consists of altered chlorophyll (Xanthophyll) ; in flowers the
yellow pigment usually occurs in the form of globules ; but in other cases
diffused uniformly in the cell-sap; in the yellow perigonial leaves of
Strelitzia it has the form of slender, crescentically curved and irregularly
wound fibres, which swim in the cell-sap. In the red coloured Algz, the
chlorophyll seems, at first sight, to be replaced by red colouring matter,
but according to the researches of Kiitzing (“Phycologia generals,” 21),
green chlorophyll granules are also present, only their colour is hidden by
the red colouring matter which accompanies them.

= =a

cg ss en egy
Sedge ee ech ee

im oe

Starch (Amylum) is still more widely diffused than chloro-
phyll, since perhaps no plants except the Fungi are without it.
Whether or not starch occurs in an amorphous condition is still
doubtful. Schleiden (“Grundzige” i. 181) believes that he found
it in this state in Sarsaparilla, in the rhizome of Carex arena-
ria, and in the seeds of Cardamomum minus. Tt is likewise
doubtful if it occurs in a state of solution, for I have repeatedly
seen the sap of particular cells, particularly of Zygnema, but
also of Phanerogamia, e.g. of the Potato, acquires a wine-red
colour with iodine; but this colour is no certain sign that we
have to do with starch. The form in which starch occurs uni-
versally is that of small, colourless, transparent granules, which are
accumulated in the cells without definite arrangement and in
variable number, sometimes swimming freely in the sap, some-
times slightly adherent to the wall. Their size varies from
an immeasurably small diameter to a magnitude visible even to
the naked eye (according to Payen from 2-1000ths of a milli-
metre in Chenopodium Quinoa, to 185-1000ths in the Potato) ;
granules of very different diameter occur together in the same cell,
but the maximum size of the granules of each plant is tolerably
definite.

Like the size, the form of the granules varies extremely in dif
ferent plants, and is sometimes so characteristic, that in many
instances we can determine with tolerable certainly, by the micro-
scope, the source where a starch has been obtained. Small gra-
nules are mostly regularly globular; but the larger full-grown
granules exhibit very irregular forms in many plants, being
sometimes elongated into the shape of rods, sometimes flattened,
sometimes made to assume angular form by mutual pressure,
and mostly possessing irregular projections. (See the figures

Se ot
yey se a

ae

nm teecsns ioc sas aman

oe ene
ee ee =

THE VEGETABLE CELL. 45

by Fritzsche in “ Poggend. Ann.” part 32; of Payen in “Mem.
sur les Developpements des Vegetaux,” and of Schleiden in his
“ Grundziige.”)

The starch granules of different shape agree in the
circumstance that they are not composed of one uni- 7%. 46.
form mass, but of super-imposed layers of varying
density, whence they derive a pretty appearance with
polarized light, each granule exhibiting a coloured
cross. These layers are usually much thicker on one
side of the granule than on the other (fig. 46), so that
the organic centre is far removed from the middle
point, and often closely approximated to the surface.

In fresh granules there is no cavity in the centre, but Stzeh granule of
one is readily produced by dessication and by the
contraction this produces of the internal softer substances. This
process may be traced very beautifully under the microscope, by
removing a part of the water, by strong alcohol, from fresh starch
granules taken from the Potato. In this case a little globular
cavity is first formed, and then radiating fissures soon run out in
all directions, traversing the layers of the granule at right angles.
This undoubtedly results from the middle layers being softer, and
more swollen up: by water than the outer. But the firmness is
still so great that the starch granules may be broken up into
angular pieces by pressure. Cold water does not exert any sol-
vent power over them, even when the granules are cut into thin
slices, so as to allow the water to come immediately in contact
with their inner layers. In boiling water they swell very much,
even a hundred times their original volume, without actual solu-
tion. The same effect is produced by the action of strong acids
and caustic alkalies. When iodine and water act simultaneously
either in the swollen or unswollen granules, these are coloured,
according to the amount of iodine they absorb, wine-red, indigo-
blue, and up to the deepest black blue, without undergoing any
alteration, for when the iodine is removed again by alcohol, they
again possess their original properties.

In all vegetable cells starch is a transitory product, destined to
be re-dissolved at a later period, and applied to various purposes
of nutrition. Thus the starch disappears from the albumen of the
seeds of Palms about the period of maturation, and in its place
appears a fixed oil, for which it undoubtedly furnishes the mate-

‘rial ; thus it disappears in the elaters of the Liverworts when the
spiral fibre is developed in them; and it vanishes during the ger-
mination of seeds and bulbs, serving for the nutriment of the
young plants, &. It is unknown at present in what way the
solution of the starch granules takes place in these cases ; when
artificially converted into dextrine and sugar, by diastase or sul-
phuric acid, a swelling up of the granules precedes its transforma-
tion ; but this does not happen in the living plant, for the sub-

46 ANATOMY AND PHYSIOLOGY OF

stance of the granule remains solid, and is corroded and dissolved
layer by layer from without inwards.

Observ. 1. Observation has not yet taught us anything concerning
the development of starch granules. That they are originally small and
roundish, is decided, and the laminated structure proves that the increase
of size does not depend on the expansion in all directions of the original
granule, but on gradual deposition of layers produced successively, As to
the order of the succession nothing is known. We may, with Payen and
Minter (“Bot. Zeitung,” 1845, 193), conclude, from inner layers being
softest and richest in water, that the innermost layer is the youngest ;
when we follow this hypothesis we must naturally assume that simulta-
neously with the deposition of each new layer, or rather of a new central
nucleus which is by subsequent growth to be converted into a layer,
all the old layers expand, and exhibit an increase of thickness, the more
irregular the older they grow, since the eccentricity of the organic centre
«nereases With the size of the granule. Or we may conclude, on the con-
trary, with Fritzsche and Schleiden, from the young starch granules being
globular, and the innermost layers of full-grown granules also possessing
a globular form, while the outer layers exhibit an irregular thickness on
their different sides,—further from two starch granules lying side by side,
being sometimes enclosed in a common external layer,—that the outer-
most layer is the youngest. ‘

Observ. 2. Most recent researches upon starch indicate that all the
layers of the granules are composed of one and the same substance, and
that there is no enveloping membrane contrasting with the contents.
But the latter is likewise asserted in many hands. Several German phy-
totomists, especially Sprengel, had already regarded the granular struc-
tures occurring in cells as vesicles and as the rudiments of cells, but
Turpin (“Organographie vegetale,” Mem. du Musewm, xiv.) and Raspail
(“Systeme de la Chimie organique”) were the authors who especially deve-
loped. and disseminated this theory. Turpm regarded the granular struc-
tures which occur in cells (therefore starch and chlorophyll in particular),
comprehended by him under the general name of globuline, as vesicles
which sprouted from the cell-walls, were attached by an umbilicus (for
which he took the hilum of starch granules), and grew into cells by subse-
quent enlargement. These views obtained greater diffusion in regard to the
starch granule through Raspail, and much credit was given to his state-
ment that it was composed of an outer membrane resisting the action of
water, and inner contents soluble in water and consisting of gum. All
this has been, very properly, long since forgotten, for all these statements
rest upon the most wretched observations ; but the utricular nature of
the starch grain has been again defended recently by Niigeli (“Zedéschr.
Sf wiss. Bot.” iti. 117, Ray Societys Publications, 1849, p. 183). Accord-
ing to him, the starch grain consists of a membrane and fluid contents ;
concentric layers are deposited on the inside of the membrane, as in
lignifying cells, thus the cavity of the vesicle is reduced to the smallest
possible size, being, however, always filled with fluid. Evidence for these
statements is sought for in vain, even in the plants named by Nigeli, in
which he affirms that he found the outer membrane tolerably thick and
uncolourable by iodine; wholly derived from his imagination is the fur-
ther statement that the granules rendered angular by mutual pressure

- THE VEGETABLE CELI. AT

originate together inside a chlorophyll granule; for granules of this kind
are met with in subterraneous parts,in which no trace of chlorophyll occurs,
as in the rhizome of Gloriosa superba.

In many plants the starch is replaced by tnuline, in many
parts, especially in the roots; ¢g., in the tubers of the Dahlias,
of Helianthus annwus, &c. Since we possess no re-agent for it
this substance still escapes from microscopic investigation, even
if Schleiden’s statement, that it occurs in the form of small ora-
nules, is well founded. Thus nothing is known respecting its
diffusion in the Vegetable Kingdom.

Observ. According to Mulder’s statement, inuline is coloured yellow
by iodine, this was the case with an inuline prepared from Jaraxacum
by Mulder, which I had an opportunity of examining. Other inuline,
which Prof. Chr. Gmelin prepared for me from the Dahlia, was not colour-
ed in the least by iodine, even when I added tincture of iodine to the hot
solution, before the inuline was precipitated from it.

d. Compounds dissolved in the cell-sap.

Certain compounds, most closely allied to starch and inuline,
escape from microscopic observation almost under all circum.
stances, notwithstanding their wide distribution in the Vegetable
Kingdom, because they are dissolved in the cell-sap, and there are
no means of detecting small quantities of them; these are dextrine,
gum, and sugar.

Dextrine seems to occur in all organs which are the seat of an
active process of nutrition, but can only be discovered in the ex-
pressed saps, not by microscopic observation.

Other kinds of gum, gum arabic, cherry-gum, tragacanth, the
mucilage of the seeds of Quinces, of Linseed, &e., playing a compara-
tively subordinate part, being diffused through but a small part
of the Vegetable Kingdom, are mostly to be considered as secre-
tion in the plants in which they do occur, and frequently are only
met with in isolated parenchymatous cells, as in Cactus, or in
the cells of particular organs, such as the seed-coats, or in cavities
and canals which lie between the cells, as in the Cycadeze. When
such kinds of gum completely fill the cells or canals in which
they occur, they may be detected by the dense, slimy mass which
they form with water, or by the coagulation caused by alcohol ;
in many cases, for instance in the cells of the seed-coat of Cydonia,
it is doubtful whether the gum is to be regarded as a substance
secreted in the cavity of the cell or as forming secondary layers in
it. In any case the substance of which many cell-membranes
swelling up strongly in water are composed, such as the secondary
layers of the cells of the seed coat of Collomia and of the pericarp
of Salvia, seems to be closely allied to these kinds of gum. So
long as these mucilaginous substances remain so loosely charac-

4S ANATOMY AND PHYSIOLOGY OF

terized by chemists, and no re-agents for them have been made
out, vegetable anatomists are not in a position to make out their

distribution in the Vegetable Kingdom, or their importance to
_ the plant.

Sugar is very widely distributed, especially cane-sugar, since it
not only replaces starch in many plants at the time just preced-
ing flowering, as in the Sugar-cane, the Beet, &ec., but still more
frequently precedes the deposition of starch in an organ, and is
also formed at the solution of the starch as in trees in Spring, in
germinating seeds, &c. Neither Cane nor any other sugars (grape-
sugar, fruit-sugar, mannite, &ec.) are objects for microscopic obser-
vation, since they are dissolved in the cell-sap, and we are without
re-agents for them.

Although occurring in a fluid form, the fized oils are readily
detected by their refusal to mix with water, and by their strong
refracting power, when they occur in abundance, as_ they
do principally in the seeds of many plants, more rarely in the
coats of the fruit (in Olives, many Palms, &c.), still more rarely in
the organs of vegetation (tubers of Cyperus esculentus). But
when they exist only in smaller quantities, as is the case in a great
number of plants, they escape observation by the microscope, since
they are not then separated as clearly visible drops floating in the
cell-sap, but are combined with the proteine substances. The
essential oils, when produced in large quantity, usually com-
pletely fill isolated cells, or groups of cells and cavities which lie
between cells, and then are easily discovered ; on the other hand,
in very many cases they seem to exist m such.small quantities,
that they are wholly dissolved in the cell-sap ; at all events they
cannot be visibly demonstrated in the greater number of petals.

_ All plants prepare a more or less abundant quantity of organic
acids (oxalic, malic, citric, tartaric acid, &c.), which are found only
in exceptional cases in a free condition, usually combining with
bases into acid-salts dissolved in the cell-sap ; and many of the
inorganic acids, which the plants receive from without, remain
undecomposed. The greater part of these salts, especially those of
the alkaline bases, escape microscopic examination by their solu-
tion in the cell-sap ; but there is scarcely one of the higher plants
in which some organ or other does not secrete in the cavities of its
cells insoluble salts of the earths with organic or morganic acids,
in the form of crystals. This usually takes place in cells which
contain no granular organic structures; but crystals, and chloro-
phyll granules, and the like, do not necessarily exclude one
another. In particular cells situated at the upper sides of the
leaves of many Urticaces, e.g. in Morus, Ficus elastica, &e., is
found what appears to be a peculiar organic structure (a coni-
cal projecting process of the internal wall of the cell, formed

of cellulose), upon which crystals are agglomerated as upon a
nucleus.

THE VEGETABLE CELL. 49

Crystals occur sometimes singly in a cell, or in numbers irregu-
larly scattered, combined into star-shaped
groups, or laid side by side in the form of
a bundle. Thé last condition (fig. 47) is
the most frequent, for there can scarcely
exist a plant in which have not been
found in some organs, for instance the
anther, or in the bark, such bundles of
very fine, needle-like four-sided crystals,
terminating at each end in four-sided py-
ramids (De Candolle’s “ Raphides’). The
composition of these needle-like crystals
is variously given ; according to Payen
and Schmidt, they are composed of oxa-

late of lime; according to Buchner and
Trinchinetti of phosphate of lime; ac-
cording to Nees von Esenbeck of a double Needle-shaped crystals, from the
salt of lime and magnesia with phosphoric (rine aye es uberosa. a One
acid. In very many plants, e.9g., very

beautifully in the Rhubarb-root, occur four-sided rather obtusely
pointed prisms of oxalate of lime; and moreover very frequently
mulberry-like agglomerations of rhombohedrons, which are com-
posed of carbonate of lime, more rarely of tartrate of lime (in old
Cactez), and sulphate of lime (Gin the Musaceze). (See “ Unger
on “The Formation of Crystals in Vegetable Cells,’ in the “Ann.
of the Vienna Mus.” Th. ii—Payen “ Memoires sur les Developpe-
ment des Vegetawa,’—Schmidt “Sketch of a General Method of In-
vestigating the juices and excretions of the Anvmal Organism.”)

F. ORIGIN OF THE CELL.

It is an universal law in the development of cells that the
contents are formed before the cell-membrane, and that the orga-
nization of the nitrogenous structures precedes that of the mem-
brane composed of cellulose. In plants, the formation of cells
occurs only in the cavity of older cells, and not between or upon
them.

The formation of the cells takes place in two different ways:
1, through division of older cells; 2, through the formation of
secondary cells (tochter-zellen) lying free in the cavity of a cell.

Observ. It would be superfluous to give an account of the older
theories of cell-formation which had existed up to the appearance of my
dissertation on the multiplication of vegetable cells by division, in the
year 1835, since none of them were based on any secure foundation.
Actual origination of cells had been observed only in pollen-grains and
spores, but the connexion of the formation of these with cell-formation in
general was altogether overlooked, and the emptiest conjectures had been
ventured as to the origin of cells from chlorophyll and starch-granules,

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50 ANATOMY AND PHYSIOLOGY OF

from the globules of the milk-sap, from cavities appearing in a homo-
geneous cambium, &c. Brisseau de Mirbel was the only one who sought
to solve the problem of cell-formation by careful observation of the deve-
lopment of Marchantia, but he did not succeed in finding out the mode
of development of the single cell; he believed that he discovered three
modes of formation of cells: a, between other cells (dévéloppement inter-u-
triculaire) ; b, on the surface of other cells (dévél. super-utriculaire) ; c, in
the cavity of other cells (dévél. intra-utriculaire). But all more recent
observations speak decidedly against the existence of the first two modes
of development described by Mirbel. It is true that Kiitzing (“ Phyco-
logia generalis,” 64) has assumed the formation of cells in the intercel-
lular substance, and, in like manner, Unger (“ Grundz. der Anatomie,” 45)
attributes this process to the Phanerogamia. Neither of them, however,
have any adequate evidence for the support of their views. In the dis-
sertation just spoken of, I sought to demonstrate in the Cryptogamic
water-plants, that the earlier notion of the necessity of cells originating
under the form of very small vesicles was false, and that division of the
cells takes place by the formation of partitions, which cut off the contents
of the parent-cells into separate portions; but it was not until I had
discovered the primordial utricle that I was able to trace accurately the
processes in the formation of this septum. (See the revised edition of this
paper in my “ Vermischt. Schrift.” 1845.) Before this had happened
Schleiden ( “ Beitrige zw Phytogenesis,” in. “Miiller’s Archiv.” 1838, Transl.
in “Taylor's Scientific Memoirs,” vol. ii.) had discovered the free cell-for-
mation, and declared it to be the sole mode of formation of cells, whereby
the whole theory of the development of cells was pushed into a false direc-
tion, from which it has been chiefly brought back into the right path by
Unger and Nigeli, who demonstrated the great prevalence of the process
of cell-division.

a. Division of the Cell.

The multiplication of cells by division commences by changes
undergone by the primordial utricle of the dividing cell, in conse-
quence of which partitions are developed, growing gradually
inwards from the periphery of the cell, and dividing the cavity of
the cell into two or more separate compartments. This process
is preceded in almost all cases by a formation of as many nuclei as
there are to be compartments in the mother-cell; in rare cases this
process does not occur, and the changes of the cell-contents are
limited to the phenomena which present themselves in the pri-
mordial utricle.

IT investigated the second simple process chiefly in Conferva
glomerata (“Verm. Schrift.” 623). This Conferva (pl. 1, fig. 1)
exhibits growth and cell-multiplication at two places. The prin-
cipal trunk of it consists of a row of cylindrical cells of pretty
nearly equal length; the end cell of these (a) becomes elongated
to twice the length of a cell (fig. 2), and then divided in the
middle (fig. 2 a), by a cross-partition, into two cells of the usual
length, of which the lower remains unaltered, while the upper
undergoes the same changes as the previous terminal cell, &e.

THE VEGETABLE CELL dl

While the filament is becoming longer in this way, the membranes
of many of the older cells of the filament become protruded out
sideways at the upper end (fig. 1, 6), the process growing gra-
dually into a cylindrical branch (fig. 1, c) as large as a cell, which
then becomes shut off at the base from the stem-cell, by a parti-
tion (fig. 1, d); then it presents the same elongation and the
same division in the middle (fig. 1, e) as the end cell of the stem
exhibits, thus producing a branch, which is capable of ramifying
again in like manner.

So that consequently, there are never any small cells, which
would be required to grow, formed in these plants, but every cell
possesses from the first very nearly the dimensions to which it is
subsequently fixed, only a slight growth im width occurring in it.

The process of the formation of the septum is as follows: the
cells are lined by a primordial utricle, on the inside of which
lies a layer of chlorophyll granules (pl. J, figs. 5, 6), which by the
action of substances injurious to the life of the plant, such as
alcohol, acids, &c, are separated from the primordial utricle (fig.
5 a), while this also under the same circumstances becomes de-
tached from the cell-wall. At the place where the partition is to
be formed, an annular fold grows inwards, gradually contracting
and parting off more completely the chlorophyll layer, which is
detached from the primordial utricle for some distance (fig. 5).
During this time a cellulose membrane is deposited all over the
outside of the primordial utricle (figs. 3, 4) ; so far as this lies be-
tween the outer surface of the primordial utricle and the inner
surface of the dividing cell, it constitutes the youngest and inner-
most of the secondary membranes of the latter; but at the point
at which the primordial utricle forms the fold just described this
cellulose layer is continued into the duplicature of the fold, and
thus forms an annular, thin, imperfect septum composed of two
layers. This annular fold, and the cellulose membrane lying in
it, contract more and more upon the central orifice until this dis-
appears, the chlorophyll layer and the primordial utricle are cut
off into two portions, and the cellulose membrane presents itself
as a perfect partition (fig. 6). Thus, without important disturb-
ance of the contents of the mother-cell, two secondary cells are
formed in it, which receive within them the whole contents, and
the membranes of which so far as they are in contact with the
membrane of the parent-cell serve as layers of thickening to it,
while where the secondary cells touch they appear as a partition
of the parent-cell.

Observ. 1. I have given a somewhat detailed account of these pro-
cegses, because I believe that I have traced them more minutely than
others have done. Nigeli (“ Zeitschrift.” i. 98) thinks that my description
of the parting off of the cell-contents by a fold growing inwards in the
cell, is incorrect ; he denies to the primordial utricle the characters of a
membrane, and contends that it is a layer of mucilage, not sharply de-

E2

ag ANATOMY AND PHYSIOLOGY OF

fined internally, and to the interior of which the chlorophyll granules
adhere ; he further assumes of the chlorophyll mass, that it is not sepa-
rated gradually from without inward, into two parts, but at once across
the whole cavity, and at this point the mass of mucilage at the same
time, and suddenly, forms a double layer as a cross wall, which secretes
the true cell-membrane. These statements do not all agree with nature;
the formation of the septum is gradual, the time required for its forma-
tion amounts, according to Mitscherlich (“ Monatsber. d. Akad. zu Berlin,”
Nov. 1847) to 4—5 hours,

Observ.. 2. The division of cells without previous formation of a nucleus
appears to occur only in cellular plants and especially in the Alge. It
has been observed by Nigeli in Oscillatorie, Nostochinee and Diatome.
Tt has been extended to the Phanerogamia by Unger, who thought he
saw nuclei first appear in already formed cells in many cases, a state-
ment which certainly depends on error of observation.

The division of the cells of the Desmidieze takes place in a man-
ner differing somewhat from the mode described in Conferva glo-
merata. (See “Polke, Physiol. Studien.” 1H. oft ; Ralfs’s “British
Desmidice,” 5.) In these unicellular Algze the cell consists of two
symmetrical halves, the boundary between which is sometimes
indicated only by a line (e.g., in Closteriwm), and sometimes lies
hidden in an often very considerable constriction (¢.g., Huastrum,
Cosmariwm). When the cell divides, these two halves of the cell
separate from each other, while a new portion is developed -be-
tween them, consisting of a very delicate pellicle forming a con-
tinuation of the cell-¢membrane, and this new portion becoming
divided into two parts in the middle by a septum, the original
cell is separated into two, each of which is composed of half of
the original full-grown cell, and one of the very small rudiments of
a second half. This second half grows until it equals the older
half in size and shape, whereupon the subdivision begins again.
It is doubtful whether, as Ralfs assumes, the same process occurs
also in the division of the cells of the Nostochinese, ZLygnemece
and many Conferve.

In all cases of the division of cells in plants having a stem and
leaf, and likewise in many cases among the Thallophytes, the
formation of the septa is preceded by the development of as many
nuclei as there are subdivisions formed in the cell. |The mode of
origin of these nuclei is two-fold: either they are formed anew,
or an existing nucleus separates, by division, into several.

When nuclei are formed anew in a cell, masses of protoplasm,
not sharply defined outside and increasing in density inwards, be-
come accumulated at the points where the nuclei are to appear.
Later on, especially by treating with iodine, we may observe in
the middle of each of these masses a globular body formed of
mucilaginous granular substance, more hom ogenous and frequently
far more transparent than the surrounding protoplasm, often
clearly defined externally, and almost without exception contain-

THE VEGETABLE CELL. 53

ing one or more sharply circumscribed round granules (the nucle-
oli, Kernkérperchen); the large round bodies are called the nuclei
(zellen-kern) or cytoblasts. The nuclei are usually smaller at
their first appearance than they are afterwards, so that their
growth is unmistakable. The surface of perfect nuclei appears
smooth and clearly defined, but it cannot be decided with cer-
tainty whether we ought to distinguish an enveloping membrane
and contents distinct from this, or to ascribe the membranous as-
pect of the outer layer to a somewhat greater density ; the nucleoli
always appear solid at first ; they often become hollowed out into
vesicles subsequently. The substances both of the nucleus and
of the nucleolus are coloured yellow by iodine. ‘

Observ. Opinions differ very much as to the mode in which the nucleus
is formed from the granular protoplasm. Schleiden was the first to dis-
cover the import of the nucleus and to trace its development. Accord-
ing to his views (“ Grundziige,” 3 ed. i, 208) they originate by the formation
of large granules in the protoplasm (afterwards the nucleoli) and other
granules becoming heaped up around these, and the whole becoming
more or less blended together and united into the nucleus. According to
Nigeli’s views (“ Zeitschrift. f- wiss. Bot. IIT, 100, Ray Society's Publica-
tions,” 1849, p. 166), the nucleus is not formed by the union of a consider-
able mass at once, but appears first as a very minute structure, for the
rudiments of the nuclear body may be distinguished while they are yet
little larger than the globules of the protoplasm. He also assumes that
the nucleolus is formed first, and then a layer of protoplasm is deposited
around it, which again becomes enclosed in a gelatinous membrane not
coloured by iodine ; Hofmeister (“ Hntwick. d. Pollens,” in “Bot. Zeit.” 1848,
“Die Enstehung des Embryo,” 1849, 62) declares distinctly against both
these opinions. According to his researches, the formation of the nucleus
is not preceded by the origin of nucleoli, but the nucleus presents itself
first under the form of a globular drop of a mucilaginous fluid, which be-
comes coated by a membrane over its outer surface. Im many cases no
trace of a nucleolus can be seen in the nucleus at first, and one or more
(up to twenty) are subsequently formed in it, while in other cases: one
or more granules ofa more solid substance swim in the fluid of the nucleus
from the very first, but not all of these are necessarily developed into
nucleoli, for only some of them can increase considerably in size and ac-
quire a membranous coat, the others becoming dissolved. Leaving out of
the question the membrane of the nucleus and of the nucleoli, the exist-
ence of which I never could satisfy myself, this latter view appears to me
the more correct ; that of Nageli decidedly wrong.

The second mode of origin of a nucleus, by division of a nucleus
already existing in the parent-cell, seems to be much rarer than
the new production of them, for as yet it has been observed only
in few cases, in the parent-cells of the spores of Anthoceros, in the
formation of the stomates, in the hairs of the filaments of T'rq-
descantia, &¢., by myself, Nageli, and Hofmeister ; bub ib. ig pos-
sible that this process prevails very widely, since, as the preceding
statements shew, we know very little yet respecting the origin of

54 ANATOMY AND PHYSIOLOGY OF

nuclei. Nageli thinks that the process is similar to that‘in cell-divi-
sion, the membrane of the nucleus forming a partition, and the
two portions separating in the form of two distinct cells. I was
quite as unable to see such a membranous septum and a mem-
brane on nuclei generally, and the division appeared to me to take
place by gradual constriction. According to Hofmeister’s descrip-
tion (“Hnstehwng des Embryo,’ 7) the membrane of the nucleus
dissolves, but its substance remains in the midst of the cell oe
mass of granular mucilage accumulates around it; this parts,
without being invested by a membrane, into two masses, and
these afterwards become clothed with membranes and appear as
two secondary nuclei (tochter-kerne). ,

Tt is still an unsolved question how often the process of divi-
sion of the nuclei can be repeated, whether it continues indefi-
nitely, or whether after one or more divisions it becomes extinct, and
the formation of a new nucleus becomes necessary. In the spores
of Anthoceros I found a second division, for in the parent-cell of
these a mass was formed, which first parted into two subdivisions,
and then each of these divided into two nuclei. Wimmel found the
same in the development of pollen-grains (“ Zur Eintwickelungs-
gesch d. Pollens.”—Bot. Zeit., 1850, 225). In these cases, there-
fore, a twofold division occurred. Buf, according to Wimmel,
the case is different in the formation of the parent-cell itself, for
when one of these cells is about to divide, a new nucleus is formed
in it, which becomes divided and gives rise to the development of
two secondary cells, When one of these secondary cells isto be
divided again, its nucleus takes no part in it but becomes absorbed,
a new nucleus being formed which divides, &., so that here each
nucleus is capable only of one division.

The number of nuclei that are formed in a cell varies very
much ; in most cases there are two, as in the formation of paren-
chymatous cells in the bark and the pith, in the formation of
wood-cells in the cambium ; but in elongated cells, particularly
in hairs which become articulated, half a dozen or more nuclei are
often found lying in a row. In like manner varies the proportion
of the size of the nucleus to the cavity of the cell ; in the paren-
chymatous cells of wood, in the cells of bark, and of the suberous
layer of the Dicotyledons, I found the nucleus relatively very
small ; but in the hairs, in the cells of very small organs still con-
tained within the bud, as in the young leaves, in the cells of the
apex of the root, in which organs the cells divide while they
are still very small, the nuclei occupy a very considerable portion
of the cavity of the cell.

The formation of nuclei is soon followed by that of septa be-
tween every two of the former, which is effected by the primor-
dial utricle becoming folded inwards in the same manner as de-
scribed above of Oonferva glomerata, till a partition is formed
reaching to the centre of the cell, and by the deposition of cellulose

THE VEGETABLE CELL. DD

membranes on the outside of the primordial utricles during this
process, which membranes form secondary layers to the parent-
cell where in contact with its walls, and laminze of a partition
dividing the parent-cell where in contact at the point of junction
of the two secondary cells. The number and direction of their
septa depend altogether on the number and position of the nuclei,
since each of these becomes the centre of a secondary cell. The
secondary cells accurately fill the cavity of the parent-cell, so that
there is no trace of inter-cellular passages running between them,
and the entire contents of the parent-cell are taken into the cavi-
ties of the secondary cells.

Since the membrane of the secondary cells deposited during
the formation of the partition is immeasurably thin, while the
membrane of the parent-cell usually possesses, before the division,
a perceptible, often considerable, thickness, we naturally find, on
examining a cellular tissue shortly after the division of the cells
(fig. 48), a very considerable difference in the thickness of the dif-

External layers of the rind of Cereus peruvianus.—a, cells of the rind with contracted primor-
dial utricles contracted, in part containing newly-formed septa (e). a, Cork-cells ; b, the outer layers of
the rind-cells, newly-formed by the division of the latter ; ¢, cells of the epidermis ; d, cuticle.

ferent sides of the cells composing it, for some of the walls consist
of the blended membranes of the secondary cells, others of these
united to the membranes of the parent-cells. This condition is in
a high degree striking in the investigation of many organs in
which the development has just begun, ¢.g., In the formation of a
periderm in the outer cells of the bark, where most of the newly-
formed and thin septa run parallel with the epidermis; in cam-

56 ANATOMY AND PHYSIOLOGY OF

bium, where the septa lie parallel with the bark ; In jointed hairs,
&¢. When the secondary cells exhibit no more, or but very little
growth, this condition of the thickness of the walls is permanent,
and it is possible, when the membranes of the secondary cells
have been thickened by the deposition of layers, to distinguish
their membranes clearly, in their whole course, from the mem-
brane of the parent-cell, ¢.g., in the pith of Laxodium distichwm.
On the other hand, when, as is usually the case, the secondary
cells increase much in size after their production, this condition is
changed. In these cases the membrane of the parent-cell must
naturally share in the expansion of the secondary cells, and be-
come thinner in proportion to this expansion ; in consequence of
this the membrane of the parent-cell mostly vanishes completely
from the eye, especially when the division and with it the expan-
sion of the secondary cells ig repeated.

It has already been observed that the secondary cells completely
fill the cavity of the parent-cell at their first origin. Thus, no
traces of intercellular passages can be found in tissues in the first
stages of their development. The passages are formed subsequently
by the separation of the cell-membranes at the angles of the cells,
and are not, as is usually represented, the remains of free open
spaces between globular cells which have been compressed together
in consequence of growth. In like manner the stomatal pores
are produced by the separation of two cells formed by the divi-
sion of a parent-cell.

Observ, That the formation of cells in all the organs of plants (ex-
cepting the cells originating in the embryo-sac) depends upon the division
of older cells, an opinion which could not, for a long time past, be op-
posed by any careful observer, unless he were misled by preconceived
notions. Even Meyen (“ Physiologie,” ii. 334) declares this process of cell-
formation to be very general ; but Unger (“ Linnea,’ 1841, 402; « Bot.
Zeit.,” 1844, 489), who subsequently applied to this process the term me-
resmatic cell-formation ; and Nigeli (“ Zeitschr. f. wiss. Bot.,” iii. 49, 1846),
who used the expression parietal cell- formation, more especially asserted
the general occurrence of this process of formation ; the former declaring
to be the usual mode, the latter ascribing to it the production of all vege-
tative cells,

But circumstances occurring in the division of the cells were inter-
preted in a different way from what I have done. Meyen assumed that
the cell-membrane itself became folded inwards, and in this way formed the
partition, which is decidedly incorrect. Unger thought the septum to be
originally simple, splitting afterwards into two lamelle 3 Nigeli denied
that the septum is formed gradually from without inwards, assuming that
the membrane of the secondary cell is formed simultaneously all round its
cavity, whence it would of course result, that the septum composed of the
membranes of two contiguous secondary cells would be formed at once
across through the cavity of the parent-cell. ;

In reference to this latter point, I, of course, readily admit that one
seldom succeeds in observing the gradual development of the septum in

THE VEGETABLE CELL. . 57

consequence of the folding inward of the primordial utricle, but in par-
ticular cases I have seen this process most distinctly. The description
given above rests chiefly on observations which I instituted upon the
parent-cells of pollen-grains, and in the cells which separate from each
other in the pore-cells of stomates. Mirbel (“ Recherches sur le Marchan-
tia”) detected, in 1833, that the parent-cells of the pollen-grains divide
by septa which grow from without inward ; but the correctness of this
statement was denied by Nigeli (“Hntwickelungsgesch. d. Pollens,” 1849),
who asserted that secondary cells (which he called special parent-cells)
were formed in the interior of the parent-cells, and that the seeming septa
were nothing else than the coherent walls of these cells, which were not
formed in the direction from without inwards, but simultaneously all over
the contents,—a view which was shared also by Hofmeister (“ Hntw. d.
Pollens.” —Bot. Zeit. 1848, 654). That these representations are incorrect,
and that the septa grow from without inwards (see pl. 1, fig. 8—I1,
which represent different stages of development of the parent-cells of the
pollen-grain of Althea rosea), was already stated by Unger (“ Ueb meris-
matisch. Zellenbildung bei der Entwick. der Pollenkirper.”—* Bericht. der
Ver. der Naturforsch. zu Gratz.”), and no doubt remained in my mind,
since I succeeded in bursting parent-cells of pollen-grains, the septa of
which were but half-formed, and pressing free the primordial utricle (pl. 1,
fig. 10), which was half constricted by folds passing mwards, into four
globular subdivisions connected together into a common cavity in the
centre. I have elsewhere (“ Verm. Schrift.,” 252) sought to demonstrate
that in like manner in the formation of stomates, there is no production
of secondary cells in the parent-cell, with an intercellular space running
between them, as Nigeli states. The observations of Henfrey (“ Annals
of Nat. History,” vol. xviii, 364) are in exact accordance with mine. Of
course one does not succeed in the vast majority of cases of the examina-
tion of a tissue where the cells are in course of development, in observing
the gradual growth of the septa from without inwards, and when I as-
sume that this process occurs universally, I certainly rest upon the analogy
to the few cases in which I have traced their gradual development ; but
it seems to me more logically correct to lay the main stress upon a few
accurately investigated cases, than to disregard such observations, and to
use as the basis of the theory of the development of cells, the imperfect,
though numerous, observations in which the gradual growing in of the
septum was not seen, but the mode in which it really was formed was not
perceived at all.

b. Free Cell-formation.

In free cell-formation, the cell-membrane is developed over the
surface of a mass of nitrogenous substance swimming in a fiuid
which contains formative matter, without the co-operation of a
parent-cell. In the regular course of vegetation this process of
cell-formation occurs only in the interior of cells; 1t may occur
independently of the life of the parent plant in the creation of
parasitic Fungi, Yeast cells, &e., both in the decomposing fluid of
cells and in the excreted or expressed juices. In normal free cell-
formation the secondary cells usually possess but a very small size

58 ANATOMY AND PHYSIOLOGY OF

in comparison with the parent-cell, and stand in no connexion, or,
at least, not a necessary one, with the walls of the latter.

In the Phanerogamia, free cell-formation occurs only in the
embryo-sac, in which both the rudiment of the embryo (the em-
bryonal vesicle) and the cells of the endosperm originate in this
way ; in the Cryptogamia it occurs only in the formation of spores
in the Lichens, and some of the Algze and Fungi.

The formation of free cells is usually preceded by the produc-
tion of nuclei. In this case more or less abundant accumulation
of protoplasm in the parent-cell forms the first sign of the second-
ary cells. This sometimes fills up the cavity of the parent-cell,
é.g., in the parent-cells of the spores of the Lichens, Pezize, &c.,
sometimes it occurs in relatively small quantity under the form
of cloudy masses not sharply defined, and of currents, as is usual
in the embryo-sac (pl. 1, fig. 12, s). In this protoplasm are formed
isolated points of concentration in the form of more or less trans-
parent nuclei, around which accumulates a variable portion of the
surrounding protoplasm, originally exhibiting no decided outline,
subsequently clearly defined by the formation of a primordial
utricle over the surface, which is rapidly followed by the produc-
tion of a cellulose membrane enclosing the whole nitrogenous
contents (pl. 1, figs. 18, b ; 14, 6).

Observ. To Schleiden belongs the merit of discovering free cell-formation
and the dependance in which the origin of a cell stands to the formation
of a nucleus; but he was led by this discovery to the misconception that
this was the only mode of formation of the cell occurring in nature. In
accordance with this hypothesis, the cells which were formed in other cells
would always be much smaller than the parent-cells, and would gradually
expand until they filled up the cavity of the parent-cells, and their walls
came into contact. But as the whole process could not take place in
cells which contain granular structures, such as chlorophyll or starch gra-
nules, or the like, without the displacement of these structures, and yet in
a cell of that kind in which division occurs, all these structures are still
present after the division, Schleiden invented an hypothesis to explain the
circumstance, namely, that these structures in the cavity of the parent-
cell were dissolved outside the secondary cell, and formed a-new inside it,
But as nothing of this process can be observed in nature, it alone suffices
to refute the doctrine of the universality of free cell-formation. Even
when quite recently, in consequence of Nigeli’s observations, Schleiden
(“Grundz.” 3xrd.ed. i. 213) can no longer deny that a division of cells does
occur, still he is far from acknowledging the universal diffusion of this
process, since he only refers to the older notion, retracted by Niageli
himself, that this mode of formation occurs in the Phanerogamia or in
the special parent-cells of the pollen-grains, and altogether ignores the
fact that Nigeli and others have shewn this to be the mode of formation
of all cells except those originating in the embryo-sac ; consequently,
Schleiden still ascribes to free cell-formation an influence on the develop-
ment of the plant which by no means belongs to it. When he states
that the cells are developed in this way in the embryonal vesicle, this is

THE VEGETABLE CELL. 59

decidedly false, for all recent observations agree in shewing that the em-
bryo originates from the germinal vesicle by cell-division ; not less incor-
rect is it, that free cell-formation may be traced in jointed hairs, and just
as little does it accord with the mode of formation of other plants that, as
is stated (“Grundz.” i. 211), cells are formed in cells, and the parent-cells
absorbed, in the points of the roots and shoots of the stem of Cypripe-
dium. The entire representation proves that Schleiden has never once
observed the division of a cell.

The first account given by Schleiden (“ Beitr. zwr Phytogenesis, Muller's
Archiv.” 1848) of the process of cell-formation, was faulty in many re-
spects. He altogether overlooked the important circumstance that the
nitrogenous substances were the originators of the formation of the
nuclei and the cell, for he believed the granules of protoplasm, which
he denominated mucilage (schleim), to be identical with the granules of
gum, and thought that the protoplasm might be replaced by starch, and
go through similar metamorphoses ; for he expressly mentions that starch,
or the granular mucilage replacing it, is present in the pollen-tubes, but
those substances are soon dissolved or change into sugar or gum. In the
formation of a nucleus those little mucilaginous granules were produced
in the protoplasm, then a few larger granules, and soon afterwards the
nuclei shewed themselves. When a cell was formed, it had at first the
form of a segment of a sphere, the plane side formed by the cytoblast, the
convex side by the cell-membrane. Originally the cell-membrane was
soluble in water, but it soon expanded more and more, and acquired.
greater consistence ; and its walls, with the exception of the cytoblast,
which always formed part of the wall, were composed of gelatine. The cell
now soon became so large that the cytoblast appeared only as a little body
enclosed in the lateral wall. The cytoblast might go through the whole
vital process with a cell, if it were not dissolved and absorbed in cells des-

ined to higher development, either in its place or after it has been cast
off like an useless member, in the cavity of the cell—The whole of this
account of the relation of the nucleus to the cell-membrane is incorrect.
The nucleus ig not connected with the cell-membrane’ under any circum-
stances, for it is enclosed, with all the rest of the contents of the cell, in
the primordial utricle. Its position in the newly originating cell is, as
appears to me, always central, and its form mostly globular ; it does cer-
tainly often lie upon the wall of the cell subsequently, and becomes flat-
tened. The distinction which Nigeli tries to carry out between central
and parietal nuclei is not founded in nature.

Tn Schleiden’s more recent writings the above views are partially modi-
fied. It has been recognized that the supposed gum is a nitrogenous
substance, but the name mucilage (sch/eim) has been retained ; and it is
stated of the young cell, that in many cases, after one side of it had become
elevated like a vesicle from the surface of the nucleus, a second layer is
deposited upon the free side of the latter, protecting it from solution ; the
special statement that all cells are formed in this way 1s more and more
extended to all organs of plants, even to the cambium-layer of the Dico-
tyledons (“ Anatomie der Cacteen,” 35).

Although it is a rule, which has no exception in the normal
development of the cells of all the higher plants, that nuclei make
their appearance in the nitrogenous substances which give rise to

60 ANATOMY AND PHYSIOLOGY OF

the formation of a free cell, yet this is not a necessary condition,
for it appears that every globular mass wholly or partly composed
of proteine compounds is capable of undertaking the function of
a nucleus, clothing itself with a membrane, and thus producing a
cell. This state of things is of very frequent occurrence in the
formation of the spores of the Aloz, where the whole contents of
an entire cell, ¢. g., in Vaucheria, of two copulated cells, e. g., in
Zygnema, become balled together into a globular mass, and coated
by a membrane. But it is not always such large masses, com-
posed of starch and chlorophyll granules and protoplasm, which
give rise to the formation of a spore; in very many cases smaller
globular masses of the green contents, produced by the union of a
a few chlorophyll granules, and undoubtedly also single granules
of chlorophyll, may assume this function whence Kiitzing called
the granules lying in the cells of Aleee—gonidia. This occurs in
the most striking manner in Hydrodictyon, in every cell of which
the sporidia produced from chlorophyll granules arrange them-
selves in a net-work over the whole of the inner surface of the
parent-cell, become converted into cells which grow together at
their angles, and thus collectively form a new plant.

Pollen-grains and the spores of the higher Cryptogamia exhibit
a peculiar mode of formation which connects the division of cells
with free cell-formation. After the development of four nuclei,
produced by the division of a single nucleus, accompanied simul-
taneously by the absorption of that nucleus which had given origin
to the parent-cell, the latter becomes divided into four compart-
ments (Nageli’s special parent-cells) by the folding inward of its
primordial utricle and the gradual formation of septa (which are
four or six in number, according to the relative position of the
nuclei, or, it is first divided into two segments, which are again
divided into two chambers (Nageli’s special parent-cells of the
second degree). These secondary cells are adherent to the wall of
the parent-cell wherever in contact with it, therefore wp to this
epoch only the common process of cell-division occurs (pl. 1, figs
8, 9,11). But the contents of each one of these four subdivisions
now become clothed by a new membrane (the inner pollen or spore-
coat), which, although in accurate apposition with the membrane of
the cell in the cavity of which it lies, does not adhere to it, and
subsequently secretes the outer pollen- or spore-coat. The forma-
tion of this inner pollen-cell only resembles free cell-formation in
the circumstance that its membrane is produced in the cavity of
another cell, around a primordial utricle which contains a nucleus,
without adhering to the parent-cell and forming one of its secon-
dary layers; it is distinguished from free cell-formation by the
fact that the nucleus and the primordial utricle around which the
new cell-coat is produced, belonged previously to the parent-cell,
and had caused the origin of this itself, and had not been newly-
formed for the secondary cell.

THE VEGETABLE CELL.

Il THE PHYSIOLOGICAL CONDITIONS
OF THE CELL.

Even as in anatomical respects the cell appears, on the one hand
as an independent organism, self-contained, and following its own
proper laws of formation in its development, and again, on the
other hand, in the great majority of plants, does not appear iso-
lated, but forming part of a greater whole, with which it is not
merely mechanically connected, but by the influence of which its
organic development is modified, so that its form, the position of
its pits, &e., are dependant on the condition of the neighbouring
cells,—so, in like manner, is the physiological activity of the cell,
on one hand independent of, and on the other dependant on, and
ruled by, the vital activity of the entire plant.

The vital functions of plants are separable into two great
classes, into those of nutrition and those of propagation. Both
are committed to the cells. The share which the individual cell
takes in one or both of these functions varies extremely according
to the degree of elevation of the organization of the plant.

In the lowest plants, whether, as in Protococcus, they consist
of a single cell, or as in the Confervas of rows of cells united into
a thread, each cell is capable of an independent existence. It ab-
sorbs fluid from the surrounding medium, respires, assimilates the
absorbed substances, &c.; in short, the simple vesicle suffices for
the accomplishment of all the various functions which must co-
operate in the nutritive processes of the plant. The more highly
organized a plant is, the more these various functions are com-
mitted to particular organs, the offices of which in this way be-
come special and one-sided, thus being reduced to a dependance
on the functions of the other organs. The function of absorption
is committed to the root; that of breathing and the elaboration of
the absorbed substances to the cells of the leaf, &c. With the
combination of many cells into a whole, leading a common life,
comes the necessity of a passage of the sap from one organ to
another, a circulation of the fluids, which the simply formed plant
can wholly dispense with. This movement of the sap is in great
part committed to particular cells, which take but a subordinate
part in the real busmess of nutrition.

Analogous to the more independent condition of the cell as an
organ of nutrition, in proportion as the organization of a plant is
simpler, the greater is its activity as an organ of propagation. In
the lowest plants the same cell is an organ of vegetation in the
earlier period, and an organ of fructification in the later period of
its life, germinal granules (keim-kérner) being formed in its in-
terior. In the higher plants, on the contrary, these two functions
are committed to different cells, in which case, at first, as in the

62, ANATOMY AND PHYSIOLOGY OF

Lichens, all the organs of fructification are alike, while in the more
highly developed plants a contrast between these appears, a male
and female sex, the conjunction of which is necessary for the origin
of a new plant.

Thus, the more complicated the structure of the entire plant
becomes, the more manifold the vital phenomena of the whole
display themselves, the more do we see the functions of the fun-
damental organs of the vegetable become restricted to an activity
continually becoming more special. The question here presents
itself: In what connexion does the more manifold or more special
activity of the cells stand with their organization? To this ques-
tion we have no answer. The organization of cells, the substances
of which their membranes are composed, are so uniform through-
out the whole vegetable kingdom, and all the organs of the par-
ticular plant, that as yet the connexion which must exist between
the form and organization, and the function of the cell, is alto-
gether unknown.

The function of nutrition and that of propagation form a strik-
ing contrast in all the cases in which the propagation is by spores
and seeds, since the reproduction in these, through the germination
of an organ furnishing a new plant, always causes the death of
the organ of propagation, and in many cases of the whole plant.
But there is another kind of multiplication ; the propagation by
buds, which depends on the common laws of growth, and has @#s
origin in the organs of vegetation. This mode of increase is
based on the peculiar growth of the plant. Leaving out of view
the simplest forms of the vegetable kingdom, the plant does not
consist of a fixed number of organs, developed together and at-
taining the full-growth at the same time, so as to form a com-
pleted whole, and to suffer a common death; but the organs of
the plant are developed successively in an unlimited series ; every
fresh shoot has the strength of youth, and is capable, under fa-
vourable circumstances, of entering on an independent life sepa-
rately from the other parts, and of growing into a new plant.
When even all the parts of a plant do lead a common life, they
do not collectively form one individual, but separate individuals
growing out of each other, and blended together in consequence
of their growth. It depends on the degree of organization of a
plant what part we are to regard as a special individual. When -
an uni-cellular plant divides into two cells we must regard each
cell as an individual, e.g., in the Diatomez ; in the Thallophytes,
for instance in the Lichens, each lobe of the thallus can carry on
an independent life when separated from the rest of the plant ; in
the higher plants each branch forms a repetition of the stem which
grew from the seed, and a ramified plant is looked upon as a col-
lection of as many individuals as there are branches upon it. In
this manner a branched plant (when not exhausted by the pro-
duction of seed) is ever young in its fresh shoots, although one

THE VEGETABLE CELL. 63

part after another grows old and dies; new, active individuals
sprout annually from the old ones, and there is no natural termi-
nation to the life of the whole. At the same time, the possibility
is given for a plant, in consequence of this unceasing production
of shoots, to become separated into an unlimited number of dis-
tinct plants, in a natural way by spontaneous, or by artificial, divi-
sion. From this peculiarity of the unlimited growth of a shoot
has the German language derived the expressive terms gewdchs
(a vegetable, from wachsen to grow). :

Observ. The peculiarity of their organization, and the unlimited power
of growth of plants, offer many difficulties to the definition of the dura-
tion of plants, and have given rise to many incorrect theories. Every
individual cell, and every individual organ has a determinate end to its
life, but the entire plant has not, since the individual shoots run through
their periods of development quite independently, and only share in the
weakness of age of the older organs when these are no longer able to
convey to the young shoots the needful amount of nourishment, in which
case the latter do not die from deficiency of vital energy, but are starved.
Tt therefore depends wholly upon the mode of growth of a plant whether
this occurs or not. When a plant possesses a thallus spreading horizon-
tally by the growth of its circumference, it can annually extend itself
into a larger circle, after the old parts in the centre have been long de-
cayed, as is seen in old specimens of crustaceous Lichens, in the fairy
rings caused by Fungi, &c. In like manner when a higher plant has a
creeping stem, and possesses the power of sending out lateral roots near
the vegetating points, and in this way conveys nourishment directly to
the young terminal shoots, the latter are wholly independent of the death
of the older parts of the stem and of the primary roots, and there exists
no internal cause for death in such a plant. It is truly a different plant
every new year and vegetates in a new place, but there is no definite
boundary between it and its predecessors ; such a plant is lke a wave
rolling over thé surface of a sheet of water, it is every moment another,
and yet always the same. Thousands of inconspicuous plants, of Mosses,
Grasses, Rushes, &c., have - vegetated in this manner upon peat bogs and
similar localities perhaps for thousands of years. Plants with upright
stems are placed in much more unfavourable circumstances. It has been
declared of these also, and particularly of the Dicotyledonous trees (De
Candolle, “ Physiologie Vegetate,” ii. 984), that they have no internal cause
for death, but I believe incorrectly. Examples of very old trees, such as
De Candolle collected (¢ g., Taxus 3000, Adansonia 5000, Tawodium
6000 years old, &c.), only prove, naturally, that death occurs at a very
late period in many plants placed in favourable circumstances, but not
that it does not necessarily happen. To me there appears to exist in all
trees, whether they belong to the Dicotyledons, or, like the Palms, to the
Monocotyledons, an internal cause which must produce death in time—
namely, the increasing difficulty of conveying the necessary quantity of
nourishment to the vegetating point, resulting from the elongation of the
trunk from year to year. Even when the force which carries the sap up
suffices to raise it to 200 feet or more (many Palms, as Ceroxylon andicola,
Areca oleracea, attain a height of 150—180 feet ; some Conifera, e. g.,

64 ANATOMY AND PHYSIOLOGY OF

Pinus Lamberti; Abies Douglasii, of more than 200 feet), yet a maximum
is reached there, and the terminal shoot is less perfectly nourished every
succeeding year, becomes stunted more and more,and the tree at length
dies.

Thousands of experiments have shewn that the young shoots of old
trees, when used as grafts, slips, &c., furnish as strong plants as the shoots
of young trees; even in the Palms (Phenix dactylifera) experiment has
shewn that the apex of the stem, when its vegetation begins to slacken
in an old tree, grows again into a strong tree when cut off and planted in
the earth. Not one single experiment speaks in favour of the opinion
promulgated by Knight, that all parts of a tree have a common end to
their life, and that the different trees which have been raised from one
and the same tree by grafts, decay about the same time as the parent
plant. A whole series of cultivated plants (I will only mention the
Vine, the Hop, the Italian Poplar, and the Weeping Willow) are propa-
gated by division, without any decreased power of vegetation ever being
seen, Nothing was in greater contradiction to the laws of vegetable life,
than the frequently expressed opinion, that the Potato disease of recent
years was to be ascribed to a degeneration of the Potato plant, arising
from the unceasing propagation by tubers.

If we are surprised at the intensity of the vegetative force of
individual plants, in consequence of which it re-appears with new,
unweakened energy in every bud, so must we marvel at the force
committed to so simple an organ as a cell is, if we reflect what
an influence it exerts upon the total economy of nature, as one of
the grandest of phenomena. The plant lives almost solely upon
inorganic substances ; its cells are chemical laboratories in which
these are combined into organic compounds. The plant prepares
in this way: not only the nutriment required for its own develop-
ment, but also the food on which the entire animal kingdom de-
pends. But plants not only nourish animals, they maintain the
air in a fit state for their respiration, since their breathing process
removes carbonic acid from the atmosphere and replaces it by
oxygen gas.

In all these functions the plant is throughly dependant upon
the outer world; its food is brought to it without its own co-opera-
tion, by water and air ; its respiration takes place without activity
of its own, through a penetration of its substance by gases with
which it is in contact, in consequence of a physical law ; not even
does its internal circulation of juices depend on a mechanical
activity of a circulating system; thus every necessity for motion
is removed. It is true we here and there meet with movements
in this or that organ, but these, occurring isolated in the vege-
table kingdom, are also altogether of subordinate kind in the
individual plant. They also are committed to the cells.

THE VEGETABLE CELL.

A. THE CELL AS AN ORGAN OF NUTRITION.

A. ABSORPTION OF WATERY FLUIDS.

In all plants the fluid nutriment is taken up by absorption
through cells. As the cell-membrane has no orifices, only such
matters as are actually dissolved, can be absorbed into the cell with
the water which penetrates the cell-membrane ; in hike manner,
in all the higher plants, a mechanical penetration of solid sub-
stances, even when suspended in water in the finest state of divi-’
sion, between the cells into the interior of the plant, is impossible,
since the cells which form the surface of the plant are accurately
fitted together, leaving no orifices between, except the stomates,
which never occur upon roots or parts growing under water.

Gaseous fluids, by which the cell-walls are also readily penetrable,
may in like manner be taken up by the cells situated at the sur-
face; but they can moreover penetrate between the cells, into the
interior of plants, through the stomates.

Observ. The Thallophytes possess no proper organ of absorption, but
the whole of their surface is adapted for it, and when, as in many Alge and
Lichens, they have root-like processes, these are only organs of attachment
and not special organs of absorption, In many Fungi and Lichens the sub-
stance of the thallus is composed of such loosely connected cells, that fluids
which come in contact with them penetrate between the cells into the sub-
stance of the thallus, so that the absorption is not confined to the superfi-
cial cells here. Even in the Mosses the root does not make any considerable
figure as an absorbing organ, their freely penetrable leaves bemg the chief
agents of the absorption of water. In the higher plants absorption 1s com-
mitted to the root alone, since the epidermis of the leaves and the periderm
of the other parts are much too difficult of penetration by water, to be
capable of taking up a sufficient quantity of it. This obstruction occurs
even in the root except at the young parts situated near the points. Con-
sequently, if a plant be placed in water in such a manner that its younger
roots are curved up above the surface, it dries up, while it keeps fresh
when only the younger roots (not however the extreme points, known by
the name of spongioles, alone) are immersed in water. The parts, how-
ever, the leaves particularly, protected against the entrance of fluid water,
are readily penetrable by watery vapour, and plants can in this way appro-
priate water from very moist air, as is clear from the increase of weight of
entire plants or cut twigs; this explains the great use of dew to the vege-
tation of dry, hot regions.

It has long been decided, that solid substances, insoluble in water, no
matter how finely they are powdered, e. g., the charcoal of gunpowder, can-
not pass into plants ; but this may be doubtful of the colouring matter of
Phytolacea, of decoction of log-wood, of infusion of saffron, &c., since many
observers, e. g., De Candolle, have seen such colouring matters pass into
living plants. But all accurate observations indicate that this does not
happen in uninjured roots, but only occurs when the coloured fluid comes
in contact with wounds of the plants.

EF

66 ANATOMY AND PHYSIOLOGY OF

Since the discovery of endosmose, most vegetable physiologists
have assumed it as an axiom that the absorption by cells depends
wholly and solely upon the laws of endosmose, none of the pecu-
liar forces of the living cell co-operating. All the conditions
to bring about strong endosmose do really exist in the living
vegetable cell, namely,.a membrane freely penetrable by watery
fluids ; on the one side of this the cell-sap which contams proteine
substances, dextrine, sugar, &., in solution, on the other side the
water occurring in nature, in the state of an extremely diluted
saline solution. This renders it readily explicable how cells which
are laid in water swell up rapidly, in many cases, if they contain
a concentrated protoplasm and have not firm walls (¢. g., many
pollen-grains), the powerful absorption of water causing them to
burst; and how, on the other hand, if they are laid im a strong
solution of sugar, gum, &c, they become emptied and collapse.
Under these circumstances, the assumption that the absorption of
the cells will be regulated by the laws of endosmose, is fully justi-
fied, yet special proofs of this can only be partially advanced, be-
cause on one side the phenomena of absorption are too little known
in many respects, and on the other side the theory of endosmose
is not yet perfect enough to allow of our making out in all cases
the share it has in any given phenomenon.

According to the researches of Th. de Saussure (“ Recherch.
chim. sur la Veget.” 274), healthy and diseased roots behave very
differently in reference to absorption, the latter taking up the
substances dissolved in the water in far greater quantity than the
healthy roots; the action of a poisonous substance (sulphate of
copper) had. the same result as disease of the roots, for it was not
only taken up in relatively very much greater quantity, but also
caused the absorption of other substances v hich were placed with
it for absorption by the roots, in larger proportion than occurred
in healthy roots. This condition alone would excite great doubts
of the opinion of many physiologists, e. g., of Treviranus, that the
absorption is an expression of vital force, smce it involves the
contradiction that weakening and destruction of life are combined
with an exaltation of an activity dependant on it; while it would
not be at all striking for changes to occur in a diseased or dead
cell, which would cause an alteration in the physical character of the
cell and of the phenomena standing in connexion with it. Ifthe
roots are healthy, they take up different substances in very dif-
ferent quantity from solutions of like degree of concentration
(Saussure experimented with solutions containing twelve grains
of foreign matter in forty cubic inches of water), and they separate
the fluid into a dilute solution which they absorb, and a more
concentrated which they leave behind.

Observ. The distinctions which occur in solutions of different sub-
stances, are very considerable. Sanssure in each case allowed half the

THE VEGETABLE CELL. 67

solution to be absorbed, therefore fifty parts of the dissolved substance
should have been absorbed, instead of which Polygonum Persicaria
absorbed of,—

Chloride of Potassum

= Sodium .

Nitrate of Lime .

Sulphate of Lime

Chloride of Ammonium

Acetate of Lime .

Sulphate of Copper .

Guentssyetines < Chie

lee er \ igerts cas

Humous Extractive

- Saussure tried to explain these differences.in the absorption from phy-
sical differences in the solutions, especially by the assumption that the
quantity of substance absorbed, depended on the greater or less degree or
viscidity which it imparted to the water by its solution. He regarded,
namely, the cell-membrane as a very fine filter, through which not only
would a denser solution penetrate more slowly, but which was also ca-
pable of separating the solution into a more concentrated and a more
diluted one. This explanation is certainly not sufficient, since we have
no proof that the finest filter can effect such a separation of a fluid ; and
secondly, Trinchinetti found that the quantity of substances taken up by
roots did not run parallel with the viscidity of their solutions. But there
is nothing in the result of these experiments which would be in opposi-
tion to the laws of endosmose, in particular the separation into a thinner
and a denser fluid stand in agreement with these, since many observations
(of Jerichau, Briicke) have shewn, that in endosmose the fluid does not
necessarily penetrate the septum i toto, but that in many cases a dilute
fluid or merely water goes through. We are certainly not in a condition
to state at present how one salt passes over in this, another in that, quan-
tity ; to do this it would be necessary to know the contents of the vege-
table cells and the relation in which they stand to the cell-membrane and
to the different solutions ; but no contradiction exists between the phe-
nomena referred to and endosmose. Formerly it might have been con-
cluded from the different behaviour of diseased and healthy roots, that
absorption was not a true physical process, but that the force of the living
plant was to be considered in reference to it; but not to speak of the
above-noticed contradiction that a vital act would be exalted in a dead
cell, there occur in the disease and death of a cell, two alterations which
cannot be without influence on the endosmose. In the first place the
living cell exhibits a certain tension, which is lost in the dead cell; in the
second place the primordial utricle is very readily detached from the-
inside of the cell-wall in diseased or dead cells; these two circumstances
place the cell-wall in a condition essentially different from the normal
one, and we may readily conceive that the endosmotic force of the cell-
wall becomes essentially different, and that the dead cell-membrane is
penetrated much more easily and quickly than the wall of the living cell.
There are frequent opportunities of observing the more easy penetration
of a diseased or dead cell,in microscopic investigations where tincture of
iodine is applied ; for, in the Conferve, for example, where several cells
FQ

68 ANATOMY AND PHYSIOLOGY OF

lie near together, some healthy, others diseased, the latter are very much
more quickly penetrated by the tincture of iodine.

An important question in absorption is this: are the different
substances absorbed by different plants in equal relative quan-
tity, or does one plant take up one substance, another a second
in greater abundance? Saussure, who thought the latter condi-
tion not improbable, could not find any confirmation of it in
his experiments, for the variations which he found in the absorp-
tion of different substances by different plants, were not more con-
siderable than the variations which occurred in different experi-
ments with the same plant. Trinchinetti (Sulla facolta assorbente
delle radici,) made experiments on this question, by placing differ-
ent species of plants in mixtures of two salts which do not decom-
pose one another, whereby he shewed that certainly one plant ab-
sorbed one, another plant the other salt, in preference, from a mix-
ture of nitrate of potass and common salt. Thus Mercurialis annua
and Chenopodium viride absorbed much nitre and little salt,
while Satureia hortensis and Solanum Lycospersiewm took up
much salt and little nitre, and from a mixture of sal-ammoniac
and salt Mercurialis absorbed more sal-ammoniac, while Vicia
Fa' a took more salt.

‘Tf, however, as there is every appearance, the result obtained by
Trinchinetti be correct, we can by no means deduce from it the con-
clusion that the plant possesses the power of absorbing substances
useful to it and excluding those which are injurious, for experi-
ence has amply demonstrated that it does not possess this latter
power, that it can even, as Saussure’s experiments with sulphate
of copper shew, absorb injurious substances more easily than those
which it applies to its nutrition, and we must assume that the
cause of the differences in question is to be sought in the physical
and chemical peculiarities of the particular substances, and their
relation to the cell-membrane and the cell-contents.

Observ. It is a known fact that different species of plants which grow
side by side in the same soil, to the roots of which the same nutriment is
conveyed, shew by analysis of their ashes a very different composition of
fixed constituents derived from the soil. This circumstance may be ex-
plained in two ways; either through the assumption that different species
of plants take up different constituents in unequal quantity from the
same solution, for which the experiments of Trinchinetti above-mentioned
furnish positive evidence, or through the hypothesis defended by Liebig,
that different plants take up equally, like a sponge, all that is dissolved in
water, but again reject all superfluous or injurious substances. The first
must be regarded as by far the more probable in the present state of our
knowledge, since the” second hypothesis, which is based upon Macaire-
Princep’s experiments, presently to be mentioned, that substances unfit
for the plant can be again excreted by the roots, has not been confirmed
by later researches. It is certainly not to be denied that plants possess
in the fall of the leaves a means of removing a part of the substances

THE VEGETABLE CELL. 69

taken up by their roots, but this means can only act in perennial plants,
and not in annuals. ‘

Since the roots undoubtedly possess the power of separating a saline
solution into a dilute and a concentrated, and absorbing the thinner ; and
since, according to Trinchinetti’s experiments, certain plants absorb par-
ticular salts only in very small quantity, the question arises whether, in
particular cases, the plants are in a condition to take up from a solution
water alone, with the total exclusion of the dissolved substance. We
have no definite experience on this point, but such a thing is not impro-
bable. I may mention here that formation of Fungi has been observed.
even in arsenical solutions, for arsenic is a substance so hostile to vege-
table life, that it can scarcely be supposed that any plant could maintain
its existence when it contained arsenic in its sap. It was also observed
by Vogel (Erdman and Marchand. “Jowrn.,” Bo. 25, 209), that Cereus
variabilis had taken up no copper after having been watered for ten
weeks with solution of sulphate of copper, that the copper penetrated.
just as little into the leaves of Stratiotes aloides, and that Chara vulgaris
vegetated for three weeks in a solution of sulphate of copper without
taking up this metal.

If the experiments mentioned in the foregoing cannot be ex-
plained in every single detail through the laws of endosmose, yet
there is a great probability that this will be possible in time.
We must not forget, in considering this absorption, that in the
majority of plants we have to do with an apparatus in which the
laws of endosmose cannot display themselves clearly. These can
- only be seen undisturbed where no other force is acting upon the
two fluids separated by a partition. But only the comparatively
few plants growing totally under water occur in this condition,
while the physical conditions in which the great majority of plants
are placed, must give rise to important modifications in those of
their phenomena depending upon endosmose. Since the leaves
have a large surface with a comparatively small mass, and are
provided with numerous stomates on the under side, they are
fitted to evaporate a great quantity of water. This does occur
in a surprising degree when external circumstances do not repress
the formation of vapour; thus, for example, in Hales’ experi-
ments, a sun-flower 34 feet high lost on an average a pound and
four ounces of water daily in this way, the loss rising to a pound
and fourteen ounces on a warm and dry day, from which Hales
reckoned that in comparison of the surfaces, the evaporation
was some three times as strong in this plant as in man, and in
comparison of volume seventeen times as strong. So consider-
able a loss of water cannot remain without re-action upon the
absorption of the root-cells. For since the sap in the cells of the
leaves becomes so much more concentrated through the loss of
water, their power of inducing endosmose will increase in propor-
tion, they replace the water taken from them, from the cells of the
stem, and.so this action is continued through the whole tissue of
the plant down to the roots, which strive to absorb water from

70 ANATOMY AND PHYSIOLOGY OF

without, in the same proportion as it is evaporated from the
leaves. A proof that the evaporation of the leaf actually in-
creases the absorption, is again furnished by the experiments of
Hales, according to which the quantity of water that a shoot ab-
sorbs is in direct proportion to the number of its leaves, and the
quantity of water absorbed sinks to one half when half the leaves
are cut off the shoot ; the experience also speaks in favour of it,
that during winter the root of a plant standing in the open air,
for instance, a vine or a hazel bush, begins to absorb if one of its
shoots is introduced into a hot-house, and the unfolding of its
leaves caused by the action of heat. Liebig (“Researches on the
Movement of the Jwices in the Animal Organism.” Untersuch.
tiber Saftbewegung, &c., 68) has also shewn the influence which
is exerted by evaporation at one point even in apparatus artifi-
cially contrived, and which, when it is assisted by the pressure of
the atmosphere, is capable of causing the fluid to flow through
the membrane against the laws of endosmose. In plants, this in-
fluence not only suffices to increase the absorption, and cause it
to commence under circumstances in which it did not otherwise
occur, but is even powerful enough in plants which have been
poisoned, to carry the poisoned fluid in great abundance upward
through the already dead lower part of the plant.

Observ. 1 here refer to experiments which I have made both on Firs
and Dicotyledonous trees in regard to the absorption of pyrolignite of
iron, the diffusion of which through the plant is readily perceived by the
dark colour. Young trees sawn off and placed with the cut surface in
the fluid, became filled with it, when they had white wood like the Birch,
in all their parts from below upwards, and continued to convey the fluid
upwards in this way through the lower part of the stem, after all their
cells were saturated with it and their cellmembranes were infiltrated
with it through their entire thickness: under which circumstances we can
certainly not imagine them to have retained a remnant of vitality.

a. Diffusion of the Sap in the Plant.

The mode in which the fluid taken up by the cells situated at
the surface of the rind of the root becomes diffused in the plant,
is a subject which lies in far deeper obscurity than the absorption
of the cells in contact with watery nutriment. In the lower
plants which are composed of single cells, as Protococcus, there
can be no movement of the sap, and even in such as are com-
posed of simple rows of cells, like the Confervas, each cell seems
to elaborate independently the nutriment 1 takes up. In the
Lichens we have already an indication in the different structure,
and especially in the green colour of the internal layer, that here,
where indeed no distinct organs exist, the different layers of the
thallus are endowed with unlike physiological functions ; we can
scarcely imagine this without an exchange of the juices of the

THE VEGETABLE CELL. 71

different layers, without a movement of the sap ; but we are
wholly ignorant of all that relates to this. The case is different
with the Phanerogamia, in which the different processes connected.
with the nutrition are committed to different organs ; here we at
least know somewhat more accurately the course which the sap
describes, at all events in the Dicotyledons. -

A few simple experiments leave no doubt about this. The
watery fluids are, as we have seen, absorbed by the cells lying at
the surface of the rind of the root, they flow no further, however,
in the rind, but pass into the wood, even in the small roots, and
ascend in this through the stem and branches. The proof of this —
is furnished by two facts: if the bark of a plant, best of a tree,
is cut through in a ring down to the wood, there is no interrup-
tion of the flow of sap to parts situated above the wound ; but if
the wood is cut through, the greatest care being taken to avoid
injuring the bark, that portion of the plant above the wound
dries up at once. From the wood of the stem and branches the
sap flows onwards into the leaves, and in these into their paren-
chymatous tissues, as is proved by the powerful expiration of
water vapour from them. Before the sap has reached the leaves
it is incapable of being applied to the nutrition ; consequently,
the vegetation of a plant comes to a stand still when it is de-
prived of its leaves. The sap ascending from the root to the
leaves is thence termed the crude sap. It undergoes a chemical
change in the leaves, rendering it fit to be applied to the nutrition
of the plant. To this end the sap flows backwards from the
leaves through the bark, to the lower parts, as the following cir-
cumstances testify. If the bark is cut off the stem in a ring,
the growth of that portion of the plant below the wound stands
as it were still, the stem becomes no thicker, in the Potato plant
no tubers are produced, &c.; ‘but on the other hand, the growth
above the wound is increased beyond the usual measure, very
thick layers of wood are deposited, more fruit is perfected, these
ripen sooner, &c. The deposition of starch which occurs in the
cells of the medullary rays in Autumn, goes to prove that the
portion of assimilated sap which is not used for nutrition on the
way to the root, runs back to the wood through these horizontal
medullary rays, and thus the sap describes a kind of circle, not,
indeed, in determinate vessels, but in a definite path leading
through the different parts of the plant.

Observ. It is difficult to conceive how in recent times the results of
these experiments (for the details of which reference should be made espe-
cially to Duhamel’s “Physique des arbres” and Cotta’s “ Matwrbeobach-
tungen tib. d. Bewegung des Saftes,”) could have been questioned, and the
existence of the descending current of sap in the bark denied. Certainly
it is no improvement on the theory cast aside, when the increased growth
above the annular wound is explained by artificial interruption of the
upward current of crude sap, in consequence of which the sap contaimed

i en ican ten

72 ANATOMY AND PHYSIOLOGY OF

in the upper part of the plant, must soon become greatly concentrated
and potential for development (Schleiden, “ Grundz.” 2nd ed. H. 513).
When we can succeed in fattening an animal by depriving it of a portion
of its accustomed food, this explanation may be received as satisfactory.

Mulder also (“ Physiolog. Chem.”) denies that there exists a downward
current of the sap, although he does not call in question the fact that the
nutrient matters formed in the leaves do descend. That is to say, he
assumes that the substances which the sap carries upwards are exchanged,
according to the laws of endosmose acting in the ascending sap, with
those substances which are elaborated in the leaves. If this were the case,
the latter nutrient matters must descend in the same course and through
the very cells in which the sap ascends, ¢. ¢., through the wood ; the above-
mentioned experiments demonstrate that they certamly do not, but
remain in the upper parts of the plant when this path is freely open te
them.

The different layers of the wood do not convey the sap in equal
quantity ; the outermost, youngest layers, and in stems not more
than two years old also the medullary sheath, principally preside
over the conveyance of the sap. The older a tree becomes, and
the harder the wood it possesses, the less share do the older layers
take in the conveyance of sap; hence, trees with hard wood, like
the Oak, where the sap wood exists ina circle round the stem, dry
rapidly; while in trees with soft wood, like the Birch, the central
layers of wood still carry sap, even in thick trunks.

When the’ question arises as to which elementary organs the
sap ascends in, and by what force it is lifted upwards, we arrive
at a region wherein all is still obscure, but in which so many the
more hypotheses have been ventured.

In the first place, two views stand diametrically opposed to each
other; according to one, the conveyance of the sap is committed to
the vessels; according to the other, these carry air, and the sap
flows in the cellular tissue. The adherents of the first opinion (to
which belonged Malpighi, Duhamel, Treviranus, Link) chiefly de-
pended upon the circumstance that when cut plants were placed
in coloured fluids, these became diffused through all parts of the
vascular system, a conclusion which, while referring to processes
occurring in healthy plants, takes its stand on plants placed
in most unnatural circumstances, and is now not considered
valid by any one. In like manner, no great weight can be laid
upon the phenomenon of the sap flowing from the cut vessels when
trees such as the Birch, Maple, Vine, &c., are wounded in Spring;
since these plants are in such different conditions before the un-
folding of their leaves and in later periods of their vegetation, that
a conclusion from one to the other must be regarded as inadmis-
sible. More important to the theory of the conveyance of the sap
are the experiments of Link (“Ann, de sc. natur. XXIII” 144—
“Vorles ub. Kriéuterkunde,” i, 116), according to which, plants
which have been watered for some days with a solution of ferro

THE VEGETABLE CELL. 73

cyanide of potassium, and afterwards with a solution of sulphate of
iron, had prussian blue precipitated in the vessels and not in the
wood-cells. If this result proved constant, the experiment must
be acknowledged as a conclusive evidence for the conveyance of
the sap by the vessels, but although these experiments were con-
firmed by Rominger (“ Bot. Zeit.” 1843, 177), and also have been
made repeatedly by myself with the same results in many other
cases, with Hoffman (“«b. de Organe d. Safthewegung,’—Bot. Zeit.
1850 ; Scient. Memoirs, Series 2, Vol. I), they furnished diametri-
cally opposite results, without our being able at present to deter- .
mine with certainty the cause of the difference, which possibly
may have depended on accidental injuries in the plant where the
saline solutions penetrated into the vessels.

The defenders of the idea that the vessels carry air, as the chief
of whom in recent times Schleiden is to be named (“Grundz,”
Qnd ed. II. 505), stand simply upon microscopic investigations,
since in these air is always found in the vessels. This statement,
special exceptions excluded, is undoubtedly correct.

In the first place, in regard to these exceptions, our woody
plants furnish them during the time preceding the unfolding of
the leaves in Spring. During the winter a portion of the cells of
the wood are filled with sap, the vascular system with air. Dur-
ing the rising temperature of Spring the cells become gradually
fuller and fuller of sap, and this subsequently enters the vessels
also ; now the sap flows freely from wounds in the wood, which is
not the case so long as this is contained in the cells alone; after-
wards, when the unfolding of the leaves increases very much the
evaporation of the plant, the wood is again partially emptied of
its sap, and air re-enters more particularly into the vessels. This
condition of a special fulness of sap, in which the vessels also con-
vey it, seems to be a constant condition in certain tropical climb-
ing plants, especially in Phytocrene and certain species of Cyssus
(see Gaudichaud, “ Observ. sur ’ Ascension de la seve dans uns
Liane;’?—Ann. des. sc. nat. 2nd_ser. VI. 138—Poiteau, “Sur la
Liane des Voyageurs ;’—Ann. des. se. nat. VII. 233). The sap is
exposed to a more or less considerable pressure in the vessels, so
that it mostly flows with force out of a wound; the force with
which this takes place was first determined by Hales, in his cele-
brated experiments on the Vine, which afterwards were fully con-
firmed by other experiments, more particularly by those of Briicke
(“ Pogg Ann.” 1844, No. 10). Hales found that the presence of
the sap flowing out under favourable circumstances balanced a
column of mercury twenty-six inches high. In the observations
made by Gaudichaud on Cissus hydrophora, and by Poiteau on an
unknown Cissus, the sap did not flow free from either the upper or
lower piece of the cut stem, but only out of pieces of stem which
were separated completely from the parent plants, so as to present
two open ends; here evidently the vessels were not over-filled

74 ANATOMY AND PHYSIOLOGY OF

with sap, and this was retained in the cut plant by the pressure
of the atmosphere.

If we take into consideration that the vessels, save in the said
exceptions, convey air, that in the Vine and other woody plants,
before the bleeding begins, the cells are filled with sap, which is
only afterwards taken up by the vessels, that after the unfolding of
the leaves and the great evaporation resulting from this, the ves-
sels are again emptied of sap, we cannot doubt that the cellular
tissue of the plant is the primary and principal system to which
the conveyance of the sap is committed, and that the vessels take
part in the function only under special circumstances, when the
plant is temporarily overfilled with sap, or in some very succulent
plants perhaps throughout the whole period of vegetation.

All parts of the plant do not play an equally active part in
the conveyance of the sap, for many experiments go to shew that
the organs situated at the two ends of the plant are especially
active at least in the ascent of the sap, the root fibres on the
one hand driving sap upwards, and on the other hand the leaves
attracting it.

That the ascent of the sap in Spring, before the unfolding of
the leaves, is chiefly caused by the roots driving the sap up-
wards, might be partly deduced from the fact, that the force with
which the sap flows from a wound in the stem of the Vine, is de-
pendant on the temperature in which its roots are placed (Dassen,
«“ Froriep’s Newen Notizen,’ B. 39, p. 129), partly also from the
fact that the sap does not flow merely from the cut stem of a
bleeding Vine, but the same phenomenon is displayed in the roots
down to their most slender ramifications. But that m many leafy
plants, in which the attraction of the sap by the leaves is active
as a second cause of the motion of the sap, the impulse exercised
by the roots upon the mass of the sap is also frequently necessary,
for the conveyance of a sufficient quantity of sap to the leaves,
follows from the experiments of Dassen, according to which, in
Nymphea alba and other plants, the leaves dry up, when they,
or the stems to which they belong, are placed with their cut sur-
faces in water, but they remain fresh, under similar surround-
ing conditions, when the fibrils of the roots are uninjured. Yet
that the leaves, even when only a comparatively small number
of them are left at the top of a plant, are in a condition to lift
fluids to a very considerable height in the stem, independently of
the influence of the root, follows from the experiments made by
Boucherie (“Compt. rendus,” 1849, ii. 894) upon trees, in which a
solution of pyrolignite of iron was applied to the lower ends of the
sawn-off stems.

Observations on bleeding woody plants, especially on the Vine,
prove that the activity of the roots is capable of causing the sap
not only to ascend in the cells of the stem, but also to enter into
the vessels. In like manner the activity of the leaves causes

sa na te TE OIE AAO S

THE VEGETABLE CELL. 75.

fluids, in which the open orifices of a cut stem dip, to ascend in
its vessels.

At first sight it seems very easy to give an explanation of the
ascent of the sap, both before the opening of the buds at the re-
commencement of vegetation, as well as during the period in
which the plants are clothed with leaves. During the period of
the rest of vegetation, the cells of a perennial plant are filled with
a great quantity of organic compounds, under the form of proteine
substances, sugar, gum, and more particularly of starch, which
latter is converted into sugar at the re-commencement of vegeta-
tion. In consequence of this, the cell-sap becomes capable of
setting up a powerful endosmose, and nothing seems more natural
than that the cells of the roots should absorb the water which
exists around them, and that the sap diluted by this should
be taken up by the cells above, and so be carried gradually up-
wards from one cell to another, whence the notion that endosmose
is the sole and sufficient cause of the motion of the sap, counts
many adherents even in recent times. But on closer examination
the matter appears less simple than it seemed at the first glance.
The organic compounds, especially the starch, are not, for the
most part, contained in the elongated cells of the wood, in which
the sap ascends, but more particularly in the cells of the me-
dullary rays and in those of the rind of the root, while in those
Monocotyledons, which, like the Palms, lay up a store of sugar,
gum, starch, &¢, before the time of flowering, these substances
are deposited in the parenchymatous cells of the stem. Thus the
substances which cause the setting up of the endosmose, occur in

cells which do not preside over the conveyance of the sap, while |
in the elongated cells of the wood, substances which would cause |
endosmose exist only in inconsiderable quantity, and in the ves- /
sels not at all. How then does the sap reach the wood-cells and |
vessels, and how is its motion imparted to it? I consider these *

questions as unsolved at present.

Briicke (1. c. 204) has indeed promised to demonstrate that this
process depends on the laws of endosmose, that the parenchyma-
tous cells first become densely filled with water by the help of the
soluble and expansible substances contained within them, and
then since they continually attract water, pour out that which
they cannot make room for in their cavities, with a portion of the
soluble substances, as sap, into the neighbouring vessels; but
Briicke has not yet furnished the demonstration of this. But
even if we would assume such an excretion from the cells causing
the endosmose, to be founded on the laws of that phenomenon, it
still would remain unexplained why this emptying of the paren-
chymatous cells does not take place by the most direct path, into
the intercellular passages running between them, but into the
wood-cells and vessels.

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76 ANATOMY AND PHYSIOLOGY OF

is connected with the strong evaporation; this not only causes the
sap within them to become more concentrated and thus more
capable of attracting to itself, through endosmose, the sap con-
tained in the cells of the stem (a property which the sap contained
in the leaves acquires the more since its organic, especially gummy,
compounds are formed out of inorganic substances), but, as Liebig
has shewn, the evaporation from the superficial cells causes the
flow of sap towards them by itself, and independently of the en-
dosmose they exert. The ascent of the sap through the cells of
the stem to the leaves is indeed explicable in this way; but m
what way does the activity of the leaves cause fluids in which
the open ends of the vessels of a cut stem dip, to be absorbed by
the vessels and conveyed upwards in them? That endosmose has
no share in this is self-evident, for all the conditions to induce it are
wanting. Equally insufficient is the explanation given by L. W.
Th. Bischoff (“De vera vasor. spiral. natur. et funct.” 62). Accord-
ing to his view, the air contained in the vessels is absorbed by the
sap of the cells in the different parts of the plant, and used for
the chemical transformation of their contents, consequently a fluid
which is in contact with the open mouths of vessels must be
driven into them by the pressure of the atmosphere. Were this
correct, a shoot of which the end was cut off and its vessels there-
by opened at their upper extremities, or a tree from which many
branches have been cut off, so that the vessels are in communica-
tion with the external air in many places, could not absorb fluid
into these vessels.

But in the ascent of the sap there occurs another phenomenon,
which cannot be explained by the endosmose exercised by the
cells; namely, the endeavour of the plant to carry up the sap
more especially in a perpendicular direction. It is a well-known
phenomenon that the bud which stands upon the end of a shoot
receives the most sap; that it grows out into a stronger shoot than

| those situated lower down; that of two shoots of which one is
| brought into a vertical position, the other bent sideways or down-
| wards, the growth of the former is favoured, and that of the other

interfered with. The endosmotiec force of its cells cannot be altered
by this change of position, and yet the strength of the current of
sap going to the shoot is altered.

All these explanations of the movement of the sap bear reference
only to its ascent, not one of them applies at all to the descent
of the elaborated nutrient sap. If the bark and the cambium
layer attract the nutrient matter from the leaves because their
cells contain a more concentrated sap than the cells of the leaves,
it is not evident why they cannot draw the sap directly from the
root and the wood, instead of by the long circuit through the
leaves, and why the bark is wholly incapable of carrying sap up-
wards.

Gathering all these circumstances together it seems to me to

marca erase = i aia

THE VEGETABLE CELL. TH

follow from them, that the discovery of endosmose has not solved
the problem which lies in the movement of the sap of plants,
that in all probability it really does play an important, perhaps
the principal, part in the absorption and carrying onward of the
sap; but that as yet we have no definite experiments to enable
us to determine accurately the share in the phenomenon which
is to be ascribed to this force, and that a series of phenomena
exist which are at all events at present inexplicable by endosmose.

ce. Nutrient Matters.

The question, what substances serve for the food of plants,
includes a two-fold one: 1, What elementary materials are made
use of by the plant in the formation of its substance? and 2,
What are the combinations in which those elementary materials
are taken up by plants?

The number of elementary substances which occur in plants
constantly, and, therefore, must be looked upon as necessary con-
stituents, is very inconsiderable, viz: 1, Oxygen; 2, Carbon;
3, Hydrogen; 4, Nitrogen; 5, Sulphur, 6, Phosphorus; 7, Chlorine ;
8, Iodine ; 9, Bromine ; 10, Fluorine; 11, Potassium ; 12, Sodium;
13, Calcium; 14, Magnesium; 15, Aluminium ; 16, Silictum ; 17
Tron; 18, Manganese.

Observ. These eighteen elements are not all combined in any one plant,
for not only can one be substituted for another, which is chemically nearly
allied, ¢. g., potassium for sodium, magnesium for calcium, &c., but also
particular of them, such as iodine and bromine occur only in certain
plants, of which they certainly appear to be necessary constituents. Under
these circumstances, these eighteen elementary substances are not all of
equal importance ; we must evidently lay the greatest weight upon those
which occur in all ‘plants, since these are to be regarded as the absolutely
necessary constituents. In this respect the first four mentioned stand
highest, since the principal mass of vegetable substance is composed of
them, the first three furnish the material for the formation of cell-mem-
brane, and nitrogen is a principal constituent of the proteine substances ;
sulphur and phosphorus, although contained in inconsiderable quantity in
plants, play a most important part, since they in like manner appear to be
necessary constituents for the formation of particular proteine compounds.
Tt is different with the radicles of the alkalies and earths, for not only
may one basic body be replaced by another in many cases, but even a sub-
stitution of ammonia for a fixed base is perhaps often possible. At-all
events, the latter appears to have been the case in certain Mould Fungi
in which Mulder found no fixed basic substance; but yet in any case this
condition must be regarded as a great exception, since alkalies and earths,
and indeed particular earths, are necessary to the well-being of all other
plants. The universally distributed chlorine is a necessary constituent of
certain plants, while iodine and bromine play in general a very sub-
ordinate part. Silicium, iron, and manganese are very generally diffused,
but in respect to their importance to the life of plants very little is known.

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78 ANATOMY AND PHYSIOLOGY OF

The questions, whether plants must take up from without the element-
ary substances which analysis discovers in them, or whether they have the
power of transforming the elements one ito another, to live upon pure
water, &c., are no longer worth discussion m these days. Whether it be
thought probable or not, that the elements of modern chemistry are actu-
ally elementary substances, it has beet placed beyond doubt, from Saus-
sure’s researches onwards through all accurate subsequent observations,
that no other substances occur in plants besides those which they take up
from without (see, especially, Wiegmann and Polstorff “ Ueber d. anorgan.
Bestandth. d. Pflanzen”).

Of all the elementary substances which enter into plants,
oxygen is the only one that is taken up in a pure condition;
plants can only appropriate the others out of chemical compounds,
which they for the most part decompose. Here at once arises
the question, whether the elementary substances when they are
to serve as food for plants, must be already combined into organic
compounds, or whether plants possess the power of feeding upon
inorganic compounds? On no question of vegetable physiology
has so active a strife existed as on this, especially since Liebig
(“ Chemistry applied to A griculture and Physiology”) appeared
as a defender of one of the extreme answers to it.

No universally valid answer can be given to this question. It
is beyond any doubt, that plants, if not as a whole, yet in an
overwhelming majority, possess the power of forming organic out
of inorganic substances, and that inorganic substances mostly
play the principal part in the nutrition. This is evident, both
from observations made on a large scale in free nature, and in
small artificial experiments. It is a perfectly universal expe-
rience, repeated in the same manner in the primeeval forests of
the tropics, on the peat bogs, meadows, and heaths of temperate
regions, and on the rocky soil of the Alps, that where the vege-
tation is left to itself upon a particular soil, and its products are
not removed from the ground, masses of decaying organic sub-
stances are formed, in consequence of the death of the plants, accu-
mulating from year to year, which can of course only be the case
through each generation of plants producing a greater quantity
of organic substances than it consumes. In a similar way, when
an estate is cultivated on proper principles, a certain amount of
organic substance is taken away, in the form of grain, cattle, &c.,
having its origin in the plants grown upon the estate, without
the necessity of adding organic matters from elsewhere, and
without diminishing the fruitfulness of the soil.

The experiments of Saussure algo, which are above all to be de-
pended on in questions relating to the nutrition of plants, shewed
that plants which he grew with water, in a closed space, in an
atmosphere rich in carbonic acid, increased their organic substance.
He calculated in a manner which does not indeed admit of exact-
ness, but still of an approximation: to the true condition, that a

THE VEGETABLE CELL. 72

plant which stands in a fruitful garden soil, cannot owe more
than 1-20th of its weight to the absorption of organic sub-
stances (“Recherches,” 268). An abundance of experiments which
have been made by the greatest variety of observers, have
shewn that plants grown in sand which has been heated to red-
ness, in metallic oxides, &c., all organic substances being excluded,
exhibit growth, stunted though it be, and in many cases form
flowers and fruit. It is not requisite to demonstrate more
minutely how these circumstances shew the total error of the
view, supported, indeed, less by vegetable physiologists than by
agriculturists and foresters, that plants subsist solely on the
mouldering remains of former plants and animals,

Buton the other hand, it is not yet proved, 1, that all plants
possess the power of living upon inorganic substances, and 2,
that the inorganic substances are the sole food of plants; that
the organic substances of humous only furnish a contribution to
the food of plants, in so far as they are separated into inorganic
substances by decomposition. This theory which, set up by
Ingenhouss, has found its most active supporter of late years in
Liebig, must in its one-sidedness be rejected in just the same
way as the opposite.

In the first place, it is opposed by the no small number of para-° |
sitic plants, which are capable of using for food the sap of living
plants, and indeed, in very many cases, only the sap of a particular
one, or at all events of very nearly allied plants. A very large

ortion of the parasites (the Loranthacese) agree with common
plants fully in their habit, colour, &¢., another portion consist, on
the contrary, of leafless plants not of a green colour, which bear
the same relation to the plants which feed them, as the flowers
and fruit of other plants do to their vegetative organs. ;

In the second place, there exists a very large number of plants,
which in part-resemble parasites in their exterior and in the
want of the green colour, in part possess the usual aspect, and,
which derive their nourishment only from vegetable or animal \
substances in a state of decomposition. To these belong, besides } |
the numerous class of the Fungi, many Orchidew, bog-plants, &¢. /

Thirdly, the majority of other plants exhibit a stunted growth
when raised in soil totally deprived of organic substances. In
this respect, however, as the experience of agriculturists and
foresters has proved, different plants manifest extraordinarily
different necessities. While one plant, such as the fir, buck-
wheat, Spergula, Sarothamus, Erica, &c., flourish in a soil which
contains only traces of organic substances, others, like the Cereals,
require for their vigorous growth, a more or less abundant admix-
ture of mouldering substances with the earth.

These circumstances indicate that different plants have a dif
ferent behaviour in regard to their nutrition; that in some
the power of living upon inorganic substances prevails, while

80 ANATOMY AND PHYSIOLOGY OF

others require a mixed food, and, finally, to the parasites are
assigned solely the still undecomposed saps elaborated by other
plants.

Observ. From such experiments made in the rough, of course no
accurate scientific result can be deduced, these can be derived only from
experiments carefully made upon a small scale. We are by no means
without experiments on a small scale of this sort, but unfortunately
most of them have been made in a manner which renders them incapa-
ble of furnishing any useful result. To these belong all earlier attempts
to grow plants with distilled water, or water containing carbonic acid, in
sand, pieces of marble, &c., im which plants of course would not flourish,
but from which no conclusion can be drawn, since not merely the organic
matters, but all the earths, salts, &c., which they required, were with-
drawn-from the plants. In order that these experiments should furnish
any certain result, they would require to be made in such a way, that the
same species of plant would be grown in a soil which contained organic
substances, and in artificial mixtures which contained all the morganic
constituents of the fertile soil, without the admixture of any organic
constituents. In respect to this, Wiegmann, at my suggestion, made
experiments (“ Bot. Zeit.,” 1843, 801), according to which, plants raised in
soil devoid of humous grew very poorly and mostly soon died. Mulder
made a larger series of analogous experiments (* Phys. Chem.”), which like-
wise lead to the belief in the use of the organic substances contained in
arable soil, as well as of the humic acid and ulmate of ammonia arti-
ficially added to it.

Even if these experiments were still far from having decided the ques-
tion of the necessity of organic food in a definitive manner, the results are
so very concordant with those of experience on a large scale, that there
can be no doubt of their general correctness, the more, that these expe-
riments made on the smallest scale, obtain a confirmation through the
extraordinary small results which manuring with Liebig’s solely inorganic
manures has everywhere had, when comparative experiments have been
made. Instead of reforming agriculture by his manures, Liebig has
caused them to demonstrate the incorrectness of his theory of the nutri-
tion of vegetables.

Yet the humous substances in vegetable mould, do not derive their im-
portance to plants from an immediate applicability as food, but exercise
their great influence on plants principally through their relations with
the alkalies and earths, and especially with ammonia. TI shall take the
liberty of giving some of the principal results of Mulder’s researches,
since these open out a series of new points of view, which promise to
become of the greatest importance to the theory of vegetable nutrition.
According to these investigations, the substances beginning to undergo
decomposition in the earth are gradually converted into a series of
chemical compounds, first imto ulmine, then into ulmic acid, humin,
humic acid, geic acid, apocrenic, and finally into crenic acid. With the
exception of the first and third, these compounds play the part of acids,
and combine in the soil with its alkalies and earths. These acids, con-
taining no nitrogen, possess a particularly strong affinity for ammonia,
which is always met with, more or less abundantly, in combination with
them. The compounds of these acids with alkalies are readily soluble

THE VEGETABLE CELL. — — 8l

in water, those with earths and metallic oxides little or not at all so.
On the other hand, their compounds with the alkalies and ammoni
readily form double salts with the earths and metallic oxides (apocreni¢
acid is penta-basic, crenic tetra-basic); the alkalies are therefore not
only a means of rendering these acids readily soluble, but they assist in
conveying the earths into plants by absorption.

Alamina plays a special part in reference to crenic and apocrenic
acids, since it forms perfectly insoluble compounds with them, in which
the acids are preserved from decomposition, and cannot be washed away
by water; yet they are not thereby completely withheld from plants,
since these compounds are capable of decomposition by ammonia, which
is thus a means of conveying these compounds into plants very gradually,
by continuous decomposition.

Most important as the above described relation of the humous acids
to ammonia is, since their great affinity for it places them in a condition
to attract this body, so important to vegetation, from the air and from
the animal substances decomposing in the soil, and prepares them for
absorption by the roots, yet they acquire still more importance from
the fact that, according to Mulder’s researches, the continuous decom-
position of the humous substances is connected with formation of
ammonia, since the oxygen of the air is used for the higher oxidation
of the rest of their substance. The evidence that nitrogen is also con-
veyed to plants in this way, lies in an experiment of Mulder’s (“ Phys.
Chemistry”), according to which, young Bean-plants which were raised
in an atmosphere free from ammonia, in ulmic acid prepared from sugar
free from ammonia, and in wood-coal, with water free from ammonia,
yielded, on analysis, twice or thrice as much nitrogen as the seeds from
which they were raised.

That the solutions of humous substances in water are absorbed by the
roots as such, and not the products of their decomposition, it would cer-
tainly be difficult to prove, since these substances cannot be demonstrated
to exist as such in the plant, but undergo a transformation directly they
are absorbed. But:in spite of the opposite results obtained by Hartig
(Liebig’s “ Agricultural Chemistry,” 1 ed.) and Unger (“ Flora,” 1842,
241), after Saussure’s experiments (Liebig “Annal.” xlii. 275), Johnson
(“ Mitth. d. Gicon. Gesells. zw Petersburg,” 2 heft 162, extracted in Wolltt’s
“Chem. Forschungen,” 202), and Trinchinetti’s (“Sul facolta assorbente
della radici,” 55), the assumption of such absorption is the less unsafe, that
it has been long demonstrated, that roots have the power of absorbing
dissolved vegetable substances, ¢. 9., tannic acid, narcotic extracts, &e.

(See Mulder, “ Phys. Chem.”)

The inorganic compounds which are taken up by plants as food,
and which furnish them with the four principal elementary bodies
which they require for their formation, are water, carbonic acid,
and ammonia.

As the absorption of watery fuids has already been discussed,
I now turn to the consideration of carbonic acid. This, it is well
known, exists universally diffused in atmospheric air and in water.
Simple experiments prove that plants do not absorb the carbonic
acid dissolved in water, with the latter, by means of their roots,

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82 ANATOMY AND PHYSIOLOGY OF

but that their green-coloured organs, consequently their leaves in
particular, possess in a high degree, so long as they are exposed to
light, the faculty of absorbing carbonic acid from the medium, be
it air or water, in which they are placed, and of secreting oxygen
gas in its place.

We owe the more accurate knowledge of this process espe-
cially to the admirable experiments of Saussure, which have been
fully confirmed by later ones of Grischow, Boussingault, and
others. The phenomena may be summed up in the following
statements. .

When green-coloured plants are exposed to the influence of sun-
light, under water containing carbonic acid, they exhale oxygen
gas. This exhalation of oxygen does not take place in boiled
water.

When plants are exposed to the influence of sunlight in atmos-
pherie air to which carbonic acid (up to 1-12th of its volume) has
been added, they remove the carbonic acid and exhale oxygen in
its place. This absorption of carbonic acid takes place very soon.
Boussingault (“ Economie rurale,” 1. 66) placed a shoot of a Vine
bearing twenty leaves in a glass globe, and while the sun shone
upon the apparatus, drew through it in an hour fifteen litres of
atmospheric air which contained ,0004 to ,00045 of carbonic acid,
and at the exit of the air from the globe, the carbonic acid was
diminished to ,0001 or ,0002. According to Chevandier’s calcu-
lations, the trees of a forest, during the five summer months in
which they bear leaves, withdraw from the column of air standing
above the forest 1-9th of its contents of carbonic acid.

When a leafy shoot with its lower end dipping in water con-
taining carbonic acid, 1s enclosed in a glass globe, its leaves exhale
more oxygen than when its lower end is dipped in common water.
A leafy shoot still connected with a tree, enclosed in a glass globe,
increases the oxygen gas in the globe. Therefore in both cases
the carbonic acid carried up with the ascending sap into the leaves
is retained by the latter, and oxygen gas given off in proportion
to it.

The exhaled carbonic acid is not contained in the plant im the
form of gas, before its separation, for plants which contain no air,
like Conferve, or leaves from which the air has been exhausted
by the air-pump, exhale oxygen in like manner. Pieces of torn
leaves possess this function as well as entire leaves; leaves, on the
contrary, which have had their organization destroyed by pres-
sure, give off no carbonic acid, neither does the epidermis of the
leaf. The quantity of oxygen gas which leaves give off depends
upon their superficial extent and not on their mass.

The secretion of oxygen varies much in abundance under illu-
mination by different rays of the solar spectrum. According to
the researches of Draper (“Treatise on the forces whach produce
the organizationof plants,” Appendix, 177), the following amounts

THE VEGETABLE CELL. 83

of gas are set free: in red 0; in red and orange 24, 75; yellow
and green 43,75; green and blue 4,10; blue 1, 0; indigo 0. The
light here acts according to the intensity of its illuminating power ;
the chemical and heating rays of the spectrum are without effect.

Observ. ‘The amount of oxygen given off is determined by the amount
of carbonic acid furnished to the plant ; the volume of the gas given off
from the plant also corresponds to the carbonic acid taken up by it, but
the gas exhaled does not consist of oxygen alone, a more or less consi-
derable quantity of nitrogen being intermingled with it Draper (L. ©.
180) obtained the following results :—

Pinus Teda.

Experiment. Oxygen. Nitrogen.
16, 16 8, 34
27, 16 13, 84
22, 33 21, 67

Pow anwun.
90, 0 hee,
a oe 22, 10

When the experiments are made by exposing plants to the sun under
spring-water, a part of the nitrogen is doubtless derived from the water,
ag well as another part from the air contained in the air-cavities of the
plant; but these circumstances do not explain the exhalation of nitrogen
completely, for according to Draper's experiments, it takes place when
plants totally deprived of air by the air-pump are experimented on i ae
water containing no nitrogen, and the quantity of nitrogen exhaled in-
creases in proportion to the amount of oxygen during the experiment,
while the reverse must occur if this intermixture depended on a diffusion
taking place between the oxygen exhaled by the plant and the nitrogen
contained in the water and in the plant. Draper draws from his experi-
ments the conclusion that the exhalation of nitrogen, is a constant pheno-
menon, connected necessarily with the exhalation of oxygen, and conjec-
tures that it is even the primary process which first sets in operation the
decomposition of the carbonic acid, that it is to be ascribed to a decompo-
sition of a nitrogenous substance in the leaf, which exercises the function
of a ferment in the decomposition of the carbonic acid.

Boussingault (“Heonomie Rurale,” i. 5) drew the opposite conclusion
from the results of Saussure’s experiments, since in particular experi-
ments the exhalation of nitrogen was so considerable, that the nitroge-
nous contents of the plant did not suffice for it; he therefore thought
we could scarcely assume otherwise than that the nitrogen was derived
from the air contained in the water and the plant. Under these circum-
stances, a trial of these conditions by accurate experiment 1s greatly
required.

The reason that the quantity of oxygen 826 given off by the plant is
unequal to the carbonic acid taken up, is doubtless that a portion of the
oxygen gas set free in the green parenchyma of the plant, enters into
combination with oxidable substances contained in it. Many phenomena

G 2

84 ANATOMY AND PHYSIOLOGY OF

speak in favour of this. hen cut leaves of water-plants, such as Vallis-
neria, Potamogeton, Nymphea, Hydrocharis, &e., the tissue of which is
traversed by wide air passages, are exposed to light under water, the
oxygen does not flow from the surface of the leaves, but from the cut
surfaces, It is therefore evident that the gas has to overcome a certain
resistance to penetrate the epidermis, and we may fairly conclude that
in many uninjured leaves, a portion of the oxygen excreted in the green
substances is carried by the intercellular passages and vessels into the
stem and roots of the plant, and consequently arrives at parts not green,
which as will appear presently absorb oxygen ; consequently a portion of
the oxygen must be deficient, on the determination of the amount formed.
For this process speaks Dutrochet’s observation (“ Memoir” i. 340), that m
Nymphea lutea the air contained in the interior of the plant contains
less oxygen the further from the leaves it is taken ; in the roots, eight per
cent. ; in the stem, sixteen per cent. ; in the leaves, eighteen percent. In
accordance with this, stands the fact, that the vessels of the stem of the
gourd contain 27-9 to 29°8 per cent. of oxygen by day (Bischoff “de vera
vas. spir. natura,” 83), while by night no oxygen but much carbonic
acid is formed in them (Focke, “de respirat. veget.,” 21).

It may be mentioned as a curiosity, that, according to Schultz’s state-
ments (“Die Entdeckung der waluren Pflanzennahrung”), the whole theory,
that plants exhale oxygen in place of the carbonic acid taken up, rests
upon an error, for the green parts of plants do indeed decompose vegeta-
ble acids, and salts of these acids, under the influence of light, but carbonic
acid forms an exception to this. Wonderful to relate, hydro-chloric
acid, which contains no oxygen, 1s named among the acids yielding most
of it. It is unnecessary to remark that the repetition of the experi-

«ments by Boussingault, Grisebach, and Grischow, fully sustain the experi-
mental skill of a Saussure against that of the Berlin physiologist.

The absorption of carbonic acid, and exhalation of oxygen by
the green parts of plants, under the influence of light, are but a
part of the complicated relations in which plants stand to atmo-
spheric air. In order to form a conception of these, we must at
the same time investigate the behaviour of the green parts in
darkness, and of organs not of a green colour. Saussure is again
the chief guide here.

As soon as green-coloured parts are withdrawn from the in-
fluence of light, their action upon the surrounding air is converted
into the opposite, they now absorb oxygen, and exhale carbonic
acid. The amount of oxygen taken up varies in the leaves of
different plants: within twenty-four hours, from half to eight
times the volume of the leaves. The volume of the carbonic
acid exhaled, is somewhat smaller than the quantity of oxygen
taken up; when the leaves are again brought to the light, they
again exhale the oxygen which had. disappeared.

All parts not coloured green (Fungi, roots, stems, flowers, &c.),
whether exposed to light or not, take up oxygen and exhale
carbonic acid.

It is usual to apply to this absorption and exhalation of parti-

THE VEGETABLE CELL. 85

cular kinds of gas, the term respiration. Many have regarded
the term as inapt, because plants have no organ of respiration,
and the like. Let us not contest words, but enquire in what
relation these processes stand to each other and to the life of the
plant.

Plants, from what has been said, have a double respiration, one
consuming carbonic acid and exhaling oxygen by day in the green
coloured organs, and one connected with a consumption of oxygen
and a formation of carbonic acid in the green organs by night, and
in those not green by day and night. ;

The question, which of these processes predominates, whether,
on the whole, the plant consumes or forms a greater quantity of
carbonic acid, whether consequently the respiration of plants 1s
on the whole a deoxidating or an oxidating process, is again fully
cleared up by Saussure’s experiments.

When a plant is confined in a definite volume of air, the air
is found unaltered in volume and composition after an equal num-
ber of days and nights; thus the plant has formed just as much
carbonic acid by night as it has consumed in the day. But if
carbonic acid is added to the atmospheric air in which the plant
vegetates, or the plant is caused to absorb water containing car-
bonic acid, it exhales oxygen into the surrounding air.

There can be no doubt that plants in open air are in the same
position as those in the last experiment. A very considerable
quantity of carbonic acid is continually being added to the atmo-
sphere through putrefaction, combustion, the respiration of animals,
volcanic eruptions, mineral sources, &e.; this constant addition of
carbonic acid above the usual amount, is again removed from the
air by plants and replaced by oxygen. Consequently, plants do
not purify the air by increasing the proportion of oxygen im it Gf
we do not take into account that carbonic acid which is not formed
at the expense of oxygen of the air, such as that derived from vol-
canie sources), but by the removal of the carbonic acid constantly
flowing into the atmosphere, formed at the expense of atmospheric
oxygen.

In order to become acquainted with the influence which these
two kinds of respiration exercise upon the vital operations of
plants, we must investigate the phenomena that present them-
selves when one or other of these breathing processes is inter-
rupted. :

When plants are prevented, by keeping them from the light,
from absorbing carbonic acid and exhaling oxygen, their nutrition
suffers and they become etiolated. They do continue to form new
shoots at the expense of the nutriment contained in their older
parts; these are even larger than those developed under the in-
fluence of light, but weak and soft; the leaves remain small and
do not become green, the normal qualities of the saps are not pro-
duced, bitter, milky plants remain sweet, &e. Some plants will

86 ANATOMY AND PHYSIOLOGY OF

exist for months in this sickly condition, but they cannot bear it
permanently.

On the other hand, when the respiration connected with the
consumption of carbonic acid is stimulated by affording to the
plant, while exposed to light, an unusual quantity of carbonic acid,
its nutrition is rendered more active. Even when nothing but
- water and carbonic acid are given, they are able to increase their
organic substance, and the weight of this increase amounts to
something like double that of the carbon which is contained in
the absorbed carbonic acid.

Observ. In an experiment of Saussure’s, little plants of Vinca appro-
priated 217 milligrammes of carbon from the carbonic acid absorbed, and
their organic substance was increased about 531 milligrammes; two
plants of Mentha sativa consumed 159 milligrammes of carbon and in-
creased in weight about 318 milligrammes (“Lecherches,” 226).

When the respiration of plants connected with absorption of oxy-
gen and formation of carbonic acid, is interrupted by placing the
entire plant in air containing no oxygen, for example in nitrogen,
or by placing the plants under the air-pump, all their functions
at once become paralyzed. The unfolding of the leaves and buds
is checked and they rot, the leaves no longer turn towards the light ;
they no longer exhibit the alternate movements of waking and

sleeping; sensitive leaves lose their irritability (Dutrochet, “Mé
moires,” i, 361, 483); even single organs cut off from air decay while
the rest live on: for instance, roots which are covered too deeply
with earth. Plants die particularly soon when kept in air devoid of
oxygen, in the dark; for example, a Cactus—a plant generally so
obstinately retentive of vitality—died in five days (Saussure, J. ¢.
87). Plants bear being placed in such an atmosphere better when
they are exposed to the alternations of day and night, since they
exhale a small quantity of oxygen from their own substance by
day, and from this form carbonic acid at night, which is again
consumed by day. Plants are capable of holding out in this way
a long time, although certainly in a very miserable way and with-
out manifesting growth; but if the small quantity of oxygen
which they form is removed by sulphur and iron filings, or the
carbonic acid by lime water, they are unable to form these gases
a second time, and die. ,

It is clear, from the preceding facts, that the respiration of
green coloured parts during the action of light is related to the
nutrient processes of the plant, since these become abnormal when
the function is interrupted, but yet the plant can maintain its
existence a long time under these conditions. But that which
occurs in common to all parts, and which consists of absorption of
oxygen and exhalation of carbonic acid, stands in immediate rela-
tion to the life of the plant. If the chemical process, which goes
on unceasingly in all the organs of plants, through the action of

THE VEGETABLE CELL. 87

oxygen gas upon vegetable substance, be interrupted, the plant,
just like an animal, becomes asphyxiated, and death follows
quickly. If we wish to speak of a respiration 10 plants, this
oxygen-consuming breathing deserves the name far more than
the exhalation of oxygen by the green organs, connected with the
nutrient processes. In this immediate relation to life the respira-
tion of plants corresponds completely with the respiration of ani-
mals; oxygen gas is a true vital air to plants. But the behaviour
of the plant towards the atmosphere becomes the more compli-
cated, that it does not merely absorb oxygen from without, like
the animal, but also a part of that prepared in its own green
organs.

Observ. Liebig must shut his eyes to facts lying open before him, when
he persists (“Agricultural Chemistry,” 6th ed.) that the respiration consum-
ing oxygen does not exist, that the absorption of oxygen has nothing to
do with the life of plants, but is a process of oxidation, which occurs m
dead wood as in the living plant, and that the exhalation of carbonic acid
stands in no connexion with the absorption of oxygen, but that the car-
bonic acid simply rises in the stem with the water taken up by the roots,
as in a cotton wick, and so passes out into the air.

Although the great diffusion of water and carbonic acid almost
everywhere give full opportunity to plants, of appropriating the
three principal elements of their substance (carbon, hydrogen, and.
oxygen), they have not always the opportunity of absorbing the
quantity of nitrogen requisite for a vigorous development, whence
the important part which nitrogenous substances play In manur-
ing. The nitrogen of the air is a perfectly indifferent body to-
wards plants. Even Saussure indicated that plants can only take
up nitrogen in the form of solutions of organic substances or of
aminonia; the latter has been especially maintained by Liebig,
and his was the merit of demonstrating by experiment that ammo-
niacal vapours exist in atmospheric air, and that ammonia occurs
in all rain and snow water; and on the other hand, of directing
attention to the presence of abundance of ammoniacal salts in. the
ascending sap of the Maple, Birch, &e. Whether, however, as
Liebig assumes, the ammonia contained in atmospheric air suffices
to furnish the nitrogen contained in wild plants, and that an
abundant supply of ammonia from the soil is necessary to culti-
vated plants, only because it is desired to stimulate them to the
production of a great mass of the constituents of blood, is quite a,
different question. In the first place, no experiment has shewn
that plants are capable of applying to their nutrition the ammo-
- niacal vapours contained in the atmosphere ; secondly, it 1s even

doubtful whether this is the case with the ammoniacal salts which
they take up by their roots, for, according to Bouchardat (“ Re-
cherches sur la Végétation,” 24), these salts, when absorbed by
\plants in watery solutions are poisonous to them in a state of
) 1000 or 1500 fold dilution. But it-is proved by abundant expe-

ain Ma eoumbhetenes! i

Bers alee!

&8 ANATOMY AND PHYSIOLOGY OF

rience that ammoniacal salts mixed with the soil, greatly further
the growth of plants. These different results render it in the
highest degree probable that the ammoniacal salts enter into com-
binations with the constituents of the soil, which exercise a dif
ferent action upon the plants, from that of the pure salts. In this
respect the investigations of Mulder upon the humous substances
are of the highest value. According to these, carbonate of ammonia
cannot exist for any time as such in humous, but is decomposed by
the organic acids of the soil; since therefore compounds of ammonia
with sulphuric and hydrochloric acids, &c., must be converted by
the carbonate of lime in the soil into carbonate of ammonia, there
exists the highest probability, that plants always receive ammonia
in combination with the organic acids of the soil, which would
explain the difference between the poisonous action of pure ammo-
niacal salts and their favourable influence when mingled with the
soil. Moreover, it is not by any means proved that the air con-
tains enough ammonia for us to regard it as anything like a suffi-
cient source of nitrogen to plants, while Mulder’s experiments
point to a production of it in the soil; in any case the amount
contained in the soil is very considerable, according to Krocker
(Berzelius, “ Jahresbericht,’ xxvi. 265) it amounts to 4045
pounds in a layer ten inches deep extending over a hectare in
sandy soil, 20314 in argillaceous soil. From these circumstances
as well as from the experiments of Boussingault and Mulder, it in
_any case follows, that the roots and not the leaves take up the
substances which furnish plants with nitrogen, while, on the con-
trary, the leaves play the especially active part in the absorption
of carbonic acid.

d. Elaboration of the Nutriment.

We know scarcely anything of the chemical processes in the
interior of plants, on which depend the assimilation of the nutrient
matter taken up, and the gradual conversion of this into the
various compounds which the plant contains. In considering the
nutritive processes of plants, two circumstances first strike us.
1, The uncommonly great agreement of all plants in respect to the
production of a series of neutral hydrates of carbon, which furnish
the material for the solid parts of plants, as also in respect to the
formation of proteine-substances which play an active part in the
process of development of the cell; 2, an infinite variety of chemi-
eal compounds, which are deposited in the different organs of
particular. groups of plants, im spite of the uniform structure
and the agreement in the nutrient process, so far as relates to
growth.

The chemists of our days, especially Mulder, have sought to
make comprehensible the formation of such a surprising abundance
of products by bodies so simply and uniformly organized as plants

ae

“SDS

THE VEGETABLE CELL 89

are. Since the plant is a complex of closed vesicles filled with
fluid, the contents of which stand in reciprocal connexion by en-
dosmose, this structure alone affords the possibility of the forma-
tion of the most varied chemical compounds. Even if we would
suppose a plant to contain a fluid of the same composition in
all its cells, this equilibrium could not last a moment ; for on the
one side the sap in the cells of one organ would acquire more con-
sistence through evaporation, and thereby call into existence an
opposition toward the other cells, while in the cells of another
organ endosmose might cause the absorption of a thinner fluid,
and thus give rise to a flowing of the sap from this organ to the
former,—which would at once cause a multiformity of the compo-
sition spreading throughout all the organs. .When we take into
consideration, that on one side ammonia with organic compounds
are taken up by the cells, while on the other side carbonic acid is
decomposed, its carbon appropriated, and its oxygen given out,
moreover that the cell-walls act by contact upon the contents of
the cells, and that this action again differs according to the differ-
ent chemical qualities of the cell-wall and contents,—it becomes
explicable how the most manifold transformations of cell-contents
and the formation of abundance of products come to pass in the
Vegetable Kingdom, the only limitation that exists being the fact
that the elementary substances do not combine together under all
conditions.

This is all correct enough, but it does not advance us one step
in the knowledge of the processes of vegetable nutrition. When
we place the contents of all the vessels in a chemical laboratory
in a condition of reciprocal connexion, we certainly expect that
an innumerable series of chemical processes will result, but what
they will be we know not, unless we know what the contents of
each vessel consist of, and in what order and under what circum-
stances the contents of one come into operation upon the contents
of another. It is of this that we are ignorant in plants, and so
long as it remains uninvestigated, we can only set up more or
less probable conjectures.

These circumstances will be my apology for treating this sub-
ject as briefly as possible.

One of the most general phenomena, since it occurs in all
ereen-coloured plants, is, as we have seen, the absorption of car-
honic avid, and the exhalation of oxygen gas. The experiments
of Saussure demonstrate that this process stands in most iInti-

‘mate connexion with the formation of organic substances; no-

thing seemed easier than to explain this process. The neutral
compounds of the plant (sugar, gum, starch, inuline and cellulose)
are composed of carbon and the elements of water; it was only
requisite to assume that the carbonic acid was decomposed in the
leaves, its oxygen given out as gas, its carbon combined with
water, which is never wanting in the plant, and the entire pro-

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90 ANATOMY AND PHYSIOLOGY OF

cess was elucidated in the simplest way. This theory conse-
quently met with universal acceptation, and in all books the
decomposition of carbonic acid, taking place in the leaves, is
spoken of as a settled fact, but we are without one proof that
such is actually the state of the case. Liebig remarked, that it
was far more probable that it was not the difficultly decomposable
carbonic acid, but the readily decomposable water which was
separated into its elements, and its oxygen given off, while its
hydrogen entered into combination with the carbonic acid.
The result was of course the same. There is no means of testing
the correctness of either of these theories. But it is possible that
they are equally false, that the carbonic acid does not enter into
combination with the hydrogen of the water, but with another
substance contained in the plant, and that oxygen becomes free
by the decomposition of an organic substance previously formed.
The latter is the opinion of Mulder, who assumes that the plant
does not decompose carbonic acid because it is green, but while it
is becoming green; new chlorophyll is constantly forming under
the influence of light, with this originate the wax and starch
associated with it, and an excretion of oxygen is necessarily con-
nected with this; and this oxygen goes off partly in the form of
gas, and in part oxidizes the colourless chlorophyll, and converts
it into green. On the other hand, Draper, on account of the ex-
halation of nitrogen which he regards as necessary, assumes that
chlorophyll acts the part of a ferment in the process of decompo-
sition of carbonic acid, and in this itself suffers a decomposition,
in consequence of which nitrogen is set free. Thus, at the very
first step of the nutrition of vegetables, which was supposed to be
the most thoroughly investigated, opinions become divergent ;
each has a certain probability, not one is proved. The only cer-
tainty is, that carbon and water remain within the plant, and are
applied to the formation of its organized substance.

On the question of the combinations into which the absorbed
nutriment first enters, the views of chemists stand in no better
agreement. Saussure’s experiments shewed that plants to which
carbonic acid and water were afforded, acquired increase of
weight equal to about twice the weight of carbon taken up.
lt may be considered probable, as Davy assumed, that the car-
bon absorbed enters at once into a neutral combination with the
elements of water; in all probability this compound is soluble in
water; since, therefore, dextrine is found in all green coloured
organs, it is not unlikely that this, or in other cases, sugar is the
form under which the said inorganic substances combine into
organic substance.

But another probability is opposed to this notion, that the con-
stituents of water and carbon enter at once into a neutral com-
bination. All plants contain, besides the neutral substances,
organic acids, in which the oxygen bears a greater proportion to

THE VEGETABLE CELL. 91

the hydrogen than in water. Among these acids, oxalic is one
of the most widely diffused,—scarcely a plant being without it.
This acid stands very close to carbonic acid, since—supposing it
anhydrous—it contains no hydrogen, and differs only from car-
bonic acid, by containing less oxygen. It may, with Liebig
(“Agricult. Chem.,” 6th ed.), be considered very probable, that the
deoxidizing process connected with the respiration of the green
organs, does not convert the carbonic acid and water at once
into neutral compounds, but first only a partial separation of
oxygen takes place, and the carbonic acid is changed into organic
acids, first of all into oxalic, the hydrate of which, by separation
of greater amounts of oxygen gas, can be transformed into malic,
citric, and other acids. It may be assumed of all these acids
that they are capable of conversion into sugar, starch, &., by the
addition of hydrogen. If this conception is adopted, the con-
stant occurrence of vegetable acids appears a necessity for the
nutritive processes of plants; and it will explain why plants will
not flourish when they do not take up a certain quantity of basic
substances, to combine into salts with these acids. On the con-
version of an acid into a neutral substance, the base becomes
free again, can unite with a new portion of acid, and so in the
course of time, a comparatively small quantity of base may
bring about the formation of a very great quantity of neutral
compounds.

Observ. This notion of the importance of acids in the vegetable eco-
nomy, has something very attractive about it, since it appears to solve a
series of questions, but on closer xamination a number of doubts present
themselves. On the one side, the assumption that the acids are formed
by a decomposition of carbonic acid, appears in any case too general,
since in many plants with fleshy leaves, an acid is formed every night
(thus at a time when no carbonic acid is decomposed), which acid is again.
decomposed by day. Here the acid is doubtless formed through oxida-
tion of a neutral compound. On the other hand, that theory does not
perfectly explain the case of the basic substances. If these had no other
destination in the plant than the purpose of fixing free acids, it would
be all one to plants whatever base was absorbed from without ; any one
could be substituted for any other. This is certainly, in some degree,
the case with regard to bases which are very closely chemically allied,
like potash and soda, or lime and magnesia, but this substitution is only
compatible to a certain extent with the healthy growth of the plant.
Particular plants require particular bases, lime, potash, &c., and die when
they do not find them in the soil. Therefore, the specific properties of
the bases stand in a definite relation to the nutritive processes of plants,
albeit, the grounds of this relation are still unexplained. If, moreover,
the acids form these transitional stages between carbonic acid and the
neutral compounds, it is remarkable that so many plants produce an
acid, and especially carbonic acid, in far greater quantity than is neces-
sary for this purpose, depositing it, in combination with lime, in an in-
soluble condition, crystallized in the cells, and yet do not subsequently

92 ANATOMY AND PHYSIOLOGY OF

re-dissolve these crystals. It is true that nutritive substances (starch,
fixed oils, &.) are frequently produced in greater abundance than the
requirements of the moment demand, and are deposited in the cells of
particular organs, but these deposits are only temporary accumulations of
food to be made use of subsequently; those deposits of insoluble salts
appear much more likely to be intended to remove from the circuit of
active juices, compounds which are superfluous to the plant.

Again, this theory does not explain the exchange of different bases
at different periods of the age of the same organ. From the analyses
of Saussure was derived the general rule, that young organs are espe-
cially rich in soluble alkaline salts, older plants in earthy salts and
metals.

A second doctrine propounded by Liebig, is connected most closely
with this opinion as to the office of the alkalies to neutralize the organic
acids, namely, the notion that for every species of plant, the amount of
oxygen of the carbonic acid contained in its ash, in the combustion of
salts originating from vegetable acids, is constant, no matter what soil
the plant may grow upon (“Agricult. Chem.” 6th ed.). For Liebig assumes
that a plant forms no more of the acids which it produces, than is
directly requisite for its vital operations, and that these therefore take
just so much alkali as will fix these determinate quantities of acid. But
weighty objections may be opposed to this doctrine. I have already ob-
served that many plants do not produce the organic acids in that quan-
tity which they would require were these converted into neutral com-
pounds, but in very considerable superabundance, as for example, all
specimens of Cactus unceasingly deposit extraordinarily large masses of
tartrate or oxalate of lime in their cells, as insoluble crystals; the oxalic
acid of these crystals is wholly withdrawn from the nutrient operations,
yet elementary analysis would make its lime appear to exist in the state
of carbonate, while at the same time, no conclusion could be drawn from
its quantity, as to the amount of acid necessary in the nutrient processes
of these plants. Moreover, all the alkalies which appear in the ash as
carbonic salts, are not combined with organic acid in the living plant,
but in many plants crystals of carbonate of lime occur; carbonic salts are
deposited in the substance of many cell-membranes, and all cell-mem-
branes are combined with alkalies and earths ; consequently, we cannot
draw from the analysis of ashes, as Liebig assumed, a proof of that law,
and this is the less possible since, moreover, the fixed alkalies may be
replaced by ammonia.

a ae
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Whatever may be the character of the chemical action to which
neutral compounds owe their origin, it is at all events, beyond
doubt that they are produced by a deoxidizing process taking
place under the influence of light. The effect of the deoxidation
extends still further, for there can scarcely be a plant which does
not contain compounds in which the oxygen is not contained in
smaller quantity, in proportion to hydrogen, than in water, even
if it be not altogether wanting. To this class belong chlorophyll
and the wax connected with it, the incrusting substances of the
wood-cells, the fixed and essential oils, res, caoutchouc, &c.
With the exception of the fixed oils, which doubtless originate

THE VEGETABLE CELL. 93

from starch, we are ignorant from what other compounds all
these constituents are derived; yet there can be no question that
their hydrogen is originally obtained from water, and that their
origin is connected with a separation of oxygen. It is remark-
able of many of them, especially in the formation of essential oils,
how much their production is favoured by the action of strong
sunlight.

The compounds containing nitrogen stand in opposition to those
devoid of it. Though in quantity they may stand far behind the
latter, their importance in the vital phenomena of plants is not
less ; nitrogenous substances, as we have seen, line the cell as the
primordial utricle, and consequently the contents of the cells are
ordered under their immediate influence; they originate the de-
velopment of new cells, and set in action the decomposition of
carbonic acid. Doubtless these constitute but a few fragments of
the great part which these substances play in the living plant; for
many chemical processes, such as fermentation, the formation of
hydrocyanic acid and amygdalin, the conversion of starch through
diastase, &c., indicate that the first impulse to the transformation
of all vegetable compounds, is principally given by the proteine
substances. The great importance which these substances have in
the vital economy of plants, is also denoted by their anatomical
conditions, since they are contained in great abundance in all
organs destined to further development, and which are endowed
with more important physiological activity; ¢. 9., in the points of
roots, in leaf and flower-buds, pollen-grains, the embryo-sac of
the ovule, and in seeds; while in old organs, principally employed
in conveying the sap, they occur in far inferior quantity.

It is as good as certain, from what has been stated above, that
ammonia in combination with organic substances furnishes the
nitrogen requisite for the formation of the proteie substances.
In what organs and under what conditions these compounds are
formed we know not. Mulder (“Phys. Chem.”) is of opinion that
they are formed at once in the points of the roots, and are dif-
fused from here over the rest of the plant. But a determined fact
may be opposed to this. view, namely, the occurrence of salts of
ammonia in ascending crude sap, which rather indicates that the
formation of nitrogenous compounds takes place chiefly, if not en-
tirely, in the leaves.

OF the formation of the other nitrogenous compounds of plants,
such as the vegetable alkalies, indigo, We., and of their import to
the plant, we know simply nothing ; I therefore consider it super-
fluous to make any further observations on them here.

e. Secretions.

In the consideration of the nutrient process of plants, the ques-
tion presses itself upon us, whether, in the series of true formations
which the mutual action of the substances contained in the plant

ence ee a ch A RO NNO ONAN te a
I NE Ra a

94 ANATOMY AND PHYSIOLOGY OF

produce, merely products which have a definite purpose in the
nutrition an@ growth of the plant are found, or other compounds
arise at the same time, which are of no further importance in
the functions of the living plant, and must be removed from the
cells carrying on the vital functions of the plant. This question
cannot be answered with certainty so long, on the one hand, as
the nutritive process is so imperfectly known, that in regard
to the chemical processes connected with it, we possess merely
more or less hazardous hypotheses, but not any knowledge what-
ever explanatory of the details; and so long, on the other hand,
as we are unacquainted from physiological causes with the import
of a great number of chemical compounds, which occur more or less,
but yet not universally diffused throughout the Vegetable King-
dom ; é. g., of the essential oils, resin, the milk-saps, the vegetable
alkaloids, &¢., which substances are usually denominated secretions.
A large portion of these substances, in particular the essential oils,
the alkaloids, the majority of the milky juices, are in the highest
degree poisonous both to the plants which prepare them, and to
others when they are caused to absorb them. These secretions are
commonly separated from the other matters within the plant, being
either, as is frequently the case with the essential oils, enclosed_in
special cells, or contained in canals which run between the cells,
as is often the case with essential oils and resin, and universally
with the milky juices. In the majority of plants containing milky
juices, these canals are lined with a special membrane, and are
then called milk-vessels, but can scarcely be separated from mere
canals destitute of proper membranes, running between the cells,
since true milk-sap is found in the latter in many plants, as in

Rhus.

Observ. Although the theory of the milk-sap is but distantly related
to the subject of the present treatise, the cell, yet I cannot avoid touch-
ing here upon the views propounded by Schultz, since if they were con-
firmed, they would effect a complete metamorphosis of the theory of the
nutrition of plants. Schultz has striven, for a long series of years, in many
essays (especially in “ Die Natur der lebenden Pflanze,” 1823-28 ; “ Sur la
Circulation et sur les vaisseaux laticiféres dans les Plantes,” 1839 ; “ Die
Cyclose des Lebenssaftes,” 1841), to demonstrate a complete analogy be-
tween the milk-sap and the blood of animals. According to him, the milk-
sap is organized, and consists of a plasma becoming coagulated out of the
plant, and of globules which correspond to the lymph and blood corpuscles.
On the coagulation of the milk-sap, an elastic coagulum, like the fibrine of
the blood, is said to separate, which is composed of caoutchouc, pure or
mingled with wax and gum, enclosing the globules of fatty or waxy mat-
ter, the larger of which are clothed with a membrane. In addition
to caoutchouc, the plasma contains sugar, albumen, gum, and salts, in
solution.

Tn all this account of the analogous organization of the milk-sap and
the blood, there is not a word of truth. The caoutchouc, as I have de-
monstrated by the simplest experiments (“ On the milk-sap and tts motion.”

THE VEGETABLE CELL. 95

—Bot. Zeit. 1848, 563) is not dissolved in the plasma, but forms the glo-
bules, which are destitute of enveloping membrane and of any organization
whatsoever ; the fluid part of the sap contains no caoutchouc, and does
not coagulate, but dries in the air into a brittle crust, composed of gum,
which may be re-diss solved in water, whereby the original character of the
milk-sap is restored. Therefore the comparison of the milk-sap with the
blood, in regard to its organization, is in every respect a mistaken one.

According to Schultz, “the milk- -sap exhibits a double motion, an inter-
nal one and a circulation. The internal motion, observed both in freshly
effused milk-sap and in that still contained in the vessels, depends on the
molecules of the sap (by which name the globules appear to be meant), |
sometimes joining together, and sometimes separating. The same process
goes on upon the walls of the vessels, and it is most distinctly noticed
that the said union and separation takes place, in the same way, between
the molecules of the sap and those of the walls of the vessels, as between
the molecules themselves, and in fact the attraction and repulsion of the
portions of the sap take place in a definite direction, so as to communicate
a progressive movement to the whole mass of sap..

It is impossible to make worse observations, and to interpret what is
seen more incorrectly, than Schultz has done in regard to the internal move-
ment of the milk-sap. Ifthe globules are small, as is usual, they exhibit
the molecular motion of Brown, and, indeed, after having been dried up
and re-dissolved in water, just as well as when fresh; if larger, as in the
milk-sap of Sambucus Ebulus, and Musa, th ere is no molecular motion.
All the rest is pure fable.

The flowing movement is, according to Schultz’s statements, completely —
independent of external influences, and goes on in the same way in per-
fectly uninjured plants as in detached organs and in separate layers cut
off the plant, which would prove that it is not caused by mechanical
effusion of part of the sap from the walls of the vessels. It is stated that
it may often be observed in detached slices, that the sap flows onwards in
a wounded vessel into the uninjured part of it, while it flows out from
other wounds which lie in the direction of the current. Since therefore
the sap flows in one portion of the vessels from the leaves to the root, and
in another portion in the reverse direction, a kind of circulation is pro-
duced (called by Schultz Cyclosis), which, however, does not run through
a definite and perfectly circular path, but parts into numerous circular
courses, returning into themselves, in the manifold ramifications and
anastomoses of the vessels.

That the sap must be in motion in an injured plant, is self-evident, for
it is well known that it flows with force out of wounds in a lacerated
milk-vessel: which is caused, not by contraction of the vessel, but by the
pressure of the cells surrounding it, since the phenomenon presents itself
in plants wherein the canals of the milk-sap do not possess any proper
wall. ‘To make out the behaviour of the milk-sap in the vessels, the ex-
periments must necessarily be made on uninjured plants. From my own
observations,—-I, like Amici and Treviranus,—must deny its movement in
the uninjured plant. A leaf of Chelidoniwm is sufficiently transparent
when it is laid beneath the microscope with its lower surface upwards,
and covered with a drop of oil and a glass plate, to allow of the appear-
ances in the milk-vessels being seen. ‘If we examine in tl his way a leaf of

96 ANATOMY AND PHYSIOLOGY OF

an uninjured plant growing in its pot, or even a detached leaf burnt at
the cub surface of the petiole, to prevent effusion of the milk-sap, the sap,
which at first is disturbed by the motion of the leaf and the pressure to
which it is exposed in spreading it out upon the stage of the microscope,
quickly comes into a state of rest; then, if the petiole is cut off with a
pair of scissors, a most rapid current immediately commences, which goes
on till the effused sap coagulates and prevents nore from being poured
out. If the same experiment is made on the leaves of Tragopogon, in
which the milk-vessels run in tolerably parallel direction, a conviction
may soon be obtained, by cutting off first the tip and on another the
base of the leaf, that the sap always flows in the direction of the wound.
When the sap is at rest in a leaf, the slighest pressure upon. the leaf suf-
fices to produce a most rapid flowing for a few seconds, and when the
pressure 1s removed, it flows back in the opposite direction. Amici shewed.
that when, by an oblique position of the mirror of the microscope, the
sunlight was thrown upon a part of the leaf on one side of the field of
vision, the sap was set in motion, and the current was reversed when the
light was thrown upon the opposite side. These experiments place it
beyond doubt to me, that the Cyclosis has no existence, and that the move-
mant of the sap is produced by mechanical causes. The further proof of
Cyclosis found by Schultz in the currents of the protoplasm contained in
the cells, which he assumes to be the same milk-sap, contained in ramifi-
cations of the milk-vessels penetrating the cell walls, needs no word of
refutation.

Schultz derives from the pretended organization and movement of the
milk-sap, the conclusion that the latter plays the same part in plants as
the blood does in animals. He therefore calls it vital-sap (lebenssaft)
latex. 1 have shewn that the bases of his arguments are incorrect obser-
vations; but, independently of that, the milk-sap is wholly unfitted on
other accounts to serve as an universal nutrient juice. In the first place,
it only occurs in a comparatively small number of plants, and, in fact,
without a definite relation to the rest of their organization and systematic
position. Schultz, indeed, asserts the contrary, since he declares that he
hag found the milk-vessels im the majority of the families investigated by
him ; but his anatomical researches are altogether unworthy of trust, for
he mingles together the most different things. In the second place, the
composition of the milk-sap is quite unsuitable in the stated purpose.
Schultz compares the caoutchouc coagulum with the fibrine of the blood.
The comparison 1s, as shewn above, incorrect, because the caoutchouc is
not dissolved in the fluid of the milk-sap; but leaving that out of the
question, the composition and chemical properties of caoutchouc are such,
that no constituent of plants could be named less fitted for the peculiar
nutrient substance, for there does not exist an indication of a possibility
that it is capable of metamorphosis within the plant. Thirdly, the com-
position of the milk-sap varies exceedingly in different plants, and fre-
quently im closely-allied species, although most milk-saps agree in being
poisonous. Side by side with the acrid milk-sap of Euphorbia canarien-
sis stands the mild juice of £. balsamifera; beside the narcotic juice of
Papaver, the acrid juice of Chelidonium; beside the narcotic of Lactuca
virosa, &e., the innocuous juice of other species of Lactuca; beside the
frightfully poisonous juice of Antiaris toxicaria, the harmless juice of

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THE VEGETABLE CELL. 97

A. mnocua. These objections are met, it is true, by Schultz with the asser-
tion that the milk-saps of L’uphorbia, &e., are not poisonous, but that the
poisonous matter comes from reservoirs of secretion wounded at the same
time as the milk-vessels ; this, however, is a complete flight of imagina-
tion, for which not the shadow of a proof exists.

So the whole of Schultz’s theory of the milk-sap is a tissue of the most
unfounded hypotheses, offering the most glaring contradiction to positive
facts.

Though the physiological import of the secreted fluids preserved
in the interior of plants is uncertain, there is no doubt that the
purpose of those secretions which occur upon the surface of plants
might be more readily made out, if the fluids were excreted in suf.
ficient quantity to be collected. Whether such excretions oceur, is
still unknown. Here, of course, we can merely have to do with
those secretions which have a more general diffusion, since local
exudations, which only occur in particular plants, like the acids in
the glandular hairs of Cicer arietinum, the gummy secretions of
Primula, Silenew, &e., can merely serve special purposes.

Such a secretion has been attributed by many to the root,
especially by Brugmans (“De mutata humorwm in regno organico
indole,” Ludg. Batav. 1789.—Up to the time of Schleiden, a
number of authors have cited under this head a treatise by
Brugmans, “De Lolio ejusdemque varia specie ;” but this essay
seems to have no existence), who thought he discovered that cer-
tain plants do not flourish in the vicinity of certain others, e. g.,
Avena near Cardwus arvensis, wheat near Lirigeron acre, flax
near Luphorbia Peplus and Scabiosa arvensis, &c. He ascribed
this to the excretion of a watery fluid from the roots of the
weeds, having the power of corroding the roots of the cultivated
plants. These excretions were considered by others, for example
by Plenk (“Phystolog.” 43), Humboldt (“A phorism. a. d. chemisch
Physiol. d. Pflanzen.” 116), Cotta (“Naturbet. ub. Bewegung d.
Sats,” 49), as evacuation of exerements, and the utility of fallows
was deduced from the hypothesis that the excrements must be
allowed to decompose in the soil before other plants could flourish
init. But this excretion from the roots was denied by others, ¢. g.,
Hedwig, and generally, speaking, no very great value was at-
tached to it. The attention of physiologists was drawn again to
the matter by Macaire Prinsep instituting, at De Candolle’s sug-
gestion (“Mem dela Soe. de Phys. de Geneve,” v. 287), experiments
which appeared to give positive results. Macaire found, namely,
that plants which had their roots carefully dug up and placed in
water, gave out into this, chiefly during the night, organic mat-
ters, which differed according to the kind of plant, being opium-
like from the Lactuceew and the Poppy, acrid from Huphorbia,
mucilaginous from the Leguminosae, &. At the same time, he be-
lieved that he found acetate of lead taken up by the plant, again
excreted in this way, further, that in water whereinto these secre-

H

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crag

Se ce ee

i, RR

98 ANATOMY AND PHYSIOLOGY OF

tions had passed, plants of the same species would not flourish,
while other species could absorb it with impunity. From these
experiments, De Candolle drew the conclusion that these excre-
tions were to be compared with the urinary excretions of ani-
mals, and explained from the doctrine, that no organized being
could use its own excrement for food, the fact of experience, that
cultivated plants, the Cerealia for example, would not flourish for
any long uninterrupted period upon the same soil.

The repetition of these experiments by others, left no doubt
that Macaire had not gone to work with the requisite circumspec-
tion in making them. Braconnot (“ Ann. d. Chimie. et d. Phys.”
tom. Ixxii. p. 32) shewed that milk-sap was effused into water from
the roots of plants of Lactuea which had been dug out of earth,
partly in consequence of laceration, partly in consequence of
irritation; but that earth wherein erium, Euphorbia, Asclepias,
and Papaver, had grown, some of them for a series of years, was
totally devoid of such excreted matters, and that merely traces
of organic substances, neither bitter nor acrid, were met with in
it, and these he attributed to the decomposition of the rootlets.
The experiments of Walser (“Uniters. ub. d. Wurzelausscheidun-
gen,” Dissert. Tubingen, 1838) likewise gave a completely negative
result, as did also Boussingault’s (<Ann. d. Chim. et d. Phys.” 1841,
tom. i., 217). Moreover that the noxious salts absorbed are not
excreted by uninjured roots, but only extracted by the water from
injured roots, was shewn by the experiments of Unger (“Ueb.
d. Vegetat. v. Kitzbiihel.” 149), and Meyen (“Physiolog.” ti. 530),
on Lemna, and Braconnot demonstrated that Macaire had made
_aclumsy mistake in his experiments, to prove the excretion of
an absorbed salt of lead, since he overlooked that the close
bundles of roots carried the solution of the lead salt over, into the
vessel of water into which another portion of the roots of the
same plant dipped, by capillary attraction.

Under these circumstances, we must regard the secretion of an
exerementitious fluid by the roots as not proven. At the same
time, it is certainly no evidence that the roots do not excrete at
all. I lay no weight upon the reason mentioned by Schleiden,
that the endosmose of the roots must be accompanied by an
exosmose, for it is too hazardous to deduce the existence of a
second phenomenon from one of which go little is known in regard
to the forces active in it, as is the case of the absorption of the
roots. A few other circumstances perhaps. speak in favour of it.
Many experiments shew that the roots of living plants exert a
chemical influence upon organic substances placed in contact with
their roots. Trinchinetti (“sull. fac. absorb. d. radici.” 57) observed,
that a decoction of humus underwent foetid putrefaction when
left to itself, but this did not take place when the roots of living
plants were placed in it. In many cases it is observed that the
roots exercise a solvent action upon solid organic substances; thus

THE VEGETABLE CELL. 99

Gazzeri saw this in Clover; Trinchinetti saw a root of N. epeta
Cataria grow through the midst of a peach-stone, and the roots
of Viscum penetrate into the periderm and bark of a tree.
There can be no doubt, that these effects are produced by a sub-
stance excreted from the roots. Of what kind this is, we know
not; yet Becquerel (Guillemin, “Archiv. de Botanique,” i. 398) has
given an indication in this direction, since he found that roots ex.
creted a free acid (probably acetic acid), or a substance which was
converted into an acid in air. This circumstance reminds us that
Lichens which live upon limestone dissolve the latter, and form
their fruit in excavations of it, which can only be through secre-
tion of a free acid. Whether the above-mentioned effects are to
be ascribed to the free acid excreted by roots, or to the secretion
of other compounds is not made out. According to Becquerel’s
researches, this excretion of a free acid occurs not only from the
roots, but from the other parts of plants—the bulbs, tubers, buds,
and leaves. Becquerel brings it into connection with the evapo-
ration of acetic acid in human perspiration ; if this analogy were
recognized and the secretion thus interpreted as a true excretion,
there would still be no inconsistency in imagining it to exercise a
function, contributing towards the accomplishment of the pur-
poses of the living plant, even in its excreted condition,

Observ. Moldenhawer (“ Beitriige x. Anatomie d. Phanzen,” 320) ex-
pressed the opinion that the organic substances used by plants for their
nutrition, underwent a chemical decomposition by a fluid secreted from
the roots, and were thus prepared for assimilation. This theory has
been revived, in recent times, by Schultz (“ Die Lintdeckung der wahren
Phanzennahrung’). He believes that he found living plants (roots as
well as leaves) decompose solutions of the most varied organic substances,
with evolution of oxygen, before they absorbed them; thus humous-
extract becomes acid, milk-sap decomposed, and cane-sugar converted |
into starch-gum. From this he concluded that plants act on the assimi-
lated compounds in a manner analogous to that of the intestinal canal of
animals upon their food. How much of truth or error there exists on
this matter must be decided by future researches of chemists,

While some discover a removal of excrements in the secretion
of a watery fluid by the roots, others ascribe the same purpose to
an aqueous secretion through the leaves, Isolated observations
had long ago indicated that water is excreted, during the night
and morning, in the form of drops of liquid, if not from all, yet
from a great many leaves, since the drops of water which are
formed at the points and serrations of leaves; owe their origin to a
secretion, and not to the dew. This subject was especially fol-
lowed out by Trinchinetti (“On « hitherto undescribed Sunetion
of the Plant,” —Literat. blatt. zur Linnea, xi. 66) ; he found little
glands (which he called glandule periphylle) at the spots where
the excretion took place ; the fluid secreted from these, though it

H 2

109 ANATOMY AND PHYSIOLOGY OF

appeared at first like pure. water, contained organic substances,
and passed into foetid decomposition. Similar observations were
made by Rainer Graf (“ Flora,” 1840, 433).

While this excretion of water occurs only in very small amount
in most plants, many of the family of the Aroideze, especially Calla
ethiopica (Gartner, “ Beiblatter zur Flora,” 1842, 1), Arum Colo-
casia (Schmidt, in Linncea, vi. 65), evacuate water in larger quan-
tity from the points of their leaves, so that it flows off in drops ;
this occurs in the most striking degree in a plant described as
Caladium destillatorwm (“Ann. of Nat. Hist.” sec, ser. i. 188),
in which each leaf—it is true, of colossal size—gave off about halt
a pint every night. The water flows here (as in Arum Colocasia)
from an orifice in the neighbourhood of the point.of the leaf, upon
the upper surface, in which terminates a canal running along the
border of the leaf, while smaller canals, running along the prin-
cipal nerves, open into this.

The water secreted, in all these cases, contains but an extremely
small quantity of organic substance in solution,

It is probable that the secretion of water in the pitchers of
Nepenthes, Sarracenia, and Cephalotus, should be reckoned with
the above. According to Vélcker’s account (“ Ann. of Nat. Hist.”
sec. ser. iv. 128), the fluid secreted by Nepenthes contains only
0,27—0,92 per cent. of solid matter, consisting of citric and malic
acids, chlorine, potash, soda, lime, and magnesia.

We have no data which would enable us to determine accu-
rately how far this secretion of drops of fluid water is (as accord-
ing to Trinchinetti) for the purpose of evacuating substances,
which, if they remained in the plant, would exercise an injurious
influence upon its health; yet this hypothesis hardly appears
probable, when we take into account the extraordinarily small
quantity of organic compounds removed in this way, together
with the circumstance that they bear none of the characters of a
substance*beginning to suffer decomposition.

The same holds good, also, in regard to the water excreted
from the leaves in the form of vapour.. This likewise contains, as
the observations of Senebier and Treviranus shewed, an ex-
tremely small quantity of organic matter, but 1s nevertheless
capable of putrefaction. Experiments which were made by Bonnet,
Duhamel, and Treviranus (“ Phys.” i. 494), to hinder the evapora-
tion, by smearing the leaves with oil and other substances, shewed
that the leaves died. This result may, however, be just as well
attributed to a positive injurious effect of the oil, in withholding
sir, as to a suppression of the evacuation of injurious matter.
Manifold experience puts it beyond doubt that repression of the
evaporation from the leaves by unfavourable conditions of weather,
produces disease, often connected with the formation of Fungi, but
this result may be caused quite as much by a disturbance of the
normal nutrient processes of the plant connected with the evapora-

THE VEGETABLE CELL. - 101

tion of a large amount of aqueous vapour, as by the retention of an
organic substance which should have been excreted by the leaves.

J. Lvolution of heat.

With the nutritive processes of plants is connected their power
of producing heat. That plants possess this power may be de-
monstrated by simple observations, but these require great ac-
curacy and certain rules of precaution, to avoid arriving at false
conclusions ; for in determining the proper heat of plants, not
only does the mostly very small amount of heat which is capable
of raising the temperature of the plant a little above that of the
air, render great caution necessary in making the experiments,
but, under common circumstances, so much heat becomes latent,
through the active excretion of aqueous vapours from the leaves,
that the temperature of the plant, in spite of the latter producing
heat, sinks below the temperature of the surrounding air. There-
fore to arrive at accurate results, it is not merely necessary to use
a very sensitive thermometric apparatus, but also to cut off the
refrigeration by evaporation. E

That seeds when germinating, as they lie heaped in large masses,
evolve a considerable degree of heat, is a fact long known from
the malting of grain, but the cause of it was incorrectly sought
for in a process of fermentation. To Gdppert (“ Ueber Wirmeen-
twickelung on der lebenden Pflanze’”’) is due the merit of having
demonstrated that such is not the case, but that the evolution of
heat is connected with the process of germination. Seeds of very
different chemical composition (of different grains, of Hemp,
Clover, Spergula, Brassica, &¢.) made to germinate in quantities
of about a pound, became heated, at a temperature of the air of
48°—66°, to 59—120° Fahr.

It was likewise shewn by Goppert, that full-grown plants, also,
such as Oats, Maize, Cyperus esculentus, Hyoscyamus, Sedum
acre, &¢., laid together in heaps, and covered with bad conductors
of heat, cause a thermometer placed among them to rise about
2°—7° (Spergula as much as 22°) akove the temperature of the
air. Dutrochet succeeded, with the help of Becquerel’s thermo-
electric needle, in demonstrating an evolution of heat in plants
standing alone (“ Ann. d. se. nat.” 1839, ii.77) ; but here the cold of
evaporation must be cut off by placing the plant in an atmosphere
completely saturated with water. Under these circumstances, the
temperature of all vegetating parts, the roots, the leaves, the
young juicy shoots (but not those of hard wood), were elevated
from about one 1-6th to 1-12th of a degree. The evolution of
heat exhibited a daily maximum and minimum; the latter oc:
curred about midnight, the former about noon, yet not at the
same hour in different plants, for the time varied from 10. A.M.
to2 PM, ~

02 ANATOMY AND PHYSIOLOGY OF

Observ. The earlier experiments to determine the temperature of
plants, by sinking thermometers in holes bored in the trunks of trees,
were completely incapable of giving a decisive answer to the question
whether plants evolve a proper heat, smce a number of circumstances,
the effect of which cannot be taken into account, are influential upon the
temperature of the tree, namely, the direct warming action of the rays
of the sun, the cooling influence of evaporation, the sometimes warm-
ing, sometimes cooling communication of the temperature of the soil,
through the medium of the ascending sap, which exercises an influence
according to the time of year, and the difference of depth to which the
roots penetrate, not to be accurately determined in isolated cases. Under
these circumstances, it is readily explicable that the experiments made by
different observers do not agree. While Nau found that the mean tem-
perature of the tree agreed with the mean temperature of the air,
Schubler found the tree 14° to 23° colder than the air in summer, and
in spring, on the contrary (March, May), about 13° to 3° warmer.
While in the experiments of Schubler, made on pretty thick trees, the
temperature of the latter never attained the extreme of the temperature
of the atmosphere, Reaumur saw slender trees heated 18° to 29° above
the temperature of the air, in the sun. Under these circumstances, the
slight evolution of heat of single plants must vanish without leaving a
trace, in the considerable, and, in some cases, discordant variations of
temperature, dependent on external influences.

A very great evolution of heat occurs in the blossom of the

Aroidess. This is considerable even in our Arum maculatum,
and, according to Dutrochet’s researches (“ Comptes rendus,” 1839,
695), rises to 25°—27° above the temperature of the air. But this
phenomenon is seen ia far higher degree in Colocasia _odora, in
which plant it has been investigated by Brongniart (“Nowv. Ann.
d. Muséum,” iii), Vrolik and Vriese (“ Ann. des Se. Nat.” sec. ser.
v. 134), and Van Beek and Bersgma (“Obs. thermo-elect. s. Vélév.
de temperat. des fleurs d. Colocas. odor.” 1838). These last ob-
servers found the maximum of heat 129°, when the temperature of
the air was 79°. The seat of the strongest evolution of heat
alters during the time of flowering ; namely, after the spathe has
opened, the anthers manifest the greatest heat ; they begin to
cool down with the emission of the pollen, after which the upper
part of the spadix, covered with abortive stamens, grows warm.

Similar observations—not, however, made with the thermo-
meter, and therefore not fitted to give an accurate determination
of the heat given off by flowers—have been made on Arum
italicwm, A. Dracunculus, Caladiwm viviparum, C. pinnati-
jfidum, and Calla cethiopica, by Saussure, Goppert, Schultz, Tre-
viranus, Gartner, and others.

The evolution of heat in the blossom of the Aroidee exhibits a
daily maximum and minimum, which, however, it is remarkable,
that different observers found to occur at different times of the
day; thus, in A. maculatum, the maximum occurred in the
morning (Dutrochet), whilst Senebier found it occur after six

THE VEGETABLE CELL, L038

o'clock in the evening; in Colocasia odora, Brongniart found the
maximum at 5 4M; Vrolik and Vriese, as well as Van Beek
and Bergsma, about 3 P.M.; and Hasskarl, in Java, at 6 AM.
(“ Tidschr. v. naturl. Gesch.” vii. letterkund Berigt. 26); as also
Hubert found, probably in the same plant, the greatest heat after
sunrise, in Madagascar.

In very few cases has evolution of heat been observed in the
blossoms of other families, Saussure, by means of an air-thermo-
meter, found the flowers of Gourds 1° to 3°, those of Bignonia
radicans 1°, of Polyanthes tuberosa 3°, and Mulder those of
Cactus grandiflorus i°—2° Fahr. warmer than the atmosphere.

There can be no doubt that the evolution of heat from flowers
results from the respiratory process connected with the formation
of a large quantity of carbonic acid. Saussure found that a
blossom of Arum maculatwm consumed in twenty-four hours,
before its heating, or after it had ceased, five times its own
volume of oxygen, while a warmer blossom consumed thirty
times, its spathe five times, the bare portion of its spadix thirty
times, and the part covered with flowers 132 times its volume of
oxygen. Vrolik and Vriese (“ Ann. d. Se. Nat. sec. sé.” xi. 62)
found the heat of a blossom of Colocasia odora increase about
9° to 10°, when brought into oxygen gas, while no evolution of
heat took place at all in carbonic acid,

In like manner, there can be no doubt that in germinating
seed, the respiration of which is equally connected with the con-
sumption of oxygen and the exhalation of carbonic acid, the evo-
lution of heat stands in connection with the formation of carbonic
acid ; but whether this source furnishes all the liberated heat, or
a part of it depends upon the vegetative process of the germina-
ting seed, cannot be.determined in the present imperfect state of
our knowledge of the chemical transformations of the substance of
the seed connected with germination.

In vegetating organs the source of heat is evidently different.
It is true, as we have seen, that oxygen is consumed and carbonic
acid formed by all organs, but since on the whole a greater quan-
tity of carbonic acid is decomposed in the green-coloured organs,
than is formed in the remaining parts, more heat must be consumed
than produced in the respirating process of vegetating organs.
But evolution of heat must be connected with the nutrient process,
for the plant forms its organic substance, if not wholly yet in great
part, from gases and liquids. Since then the growth of the plant
exhibits a daily exaltation, occurring about noon, it is quite in
accordance that the evolution of heat also should, occur in m-
creased degree at the same time.

ANATOMY AND PHYSIOLOGY OF

B,-THE CELL AS AN ORGAN OF PROPAGATION.
a. The Multiplication of Plants by Division. |

Multiplication by division occurs under different forms according
to the lower or higher stage of organization of the plants ; for the
lower it is, the more does the individual cell possess the power of
independently producing a new vegetable, whether by simple
division or by the formation of a bud; while the higher the or-
ganization of the entire plant stands, the more does the capability
of maintaining an independent vitality leave the individual cells
and become committed to smaller or larger assemblages of cells,
which must become developed into an organ of complicated
structure, before their separation from the parent plant, to ensure
their growing up into independent plants

Multiplication of plants hy division of every individual cell is
a very common. phenomenon. in the lowest forms of Algze. In the
generality of cases, the dividing cell parts into two, more rarely
into four cells, in which again the same process of multiplication
may be repeated. This is of universal occurrence in the uni-
cellular Algee, ¢. g., in the Diatomacee, Desmidiacese, &c. ; after
the division, the newly-formed cells either separate from each
other or remain joined together in colonies arranged in rows or
flat layers, more or less firmly connected by a mass of mucilagi-
nous matter, thus forming a transition towards the plants com-
posed of numbers of cells.

The same process is repeated in the many-celled Algze, for
example, in the Oscillatorieze ; in the first instance, growth of the
single individual is the result of the process of division of the
cells in these plants, but the extraordinary readiness with which
they break up into separate pieces, or, as in Nostoc, the single
cellular filaments separate from each other by solution of the
connecting mucilage, together with the power of the single pieces
to grow up again into new plants, give great facility to the mul-
tiplication of the individuals by division of their cells.

The capability of multiplying mm this way by unceasing divi-
sion of the cells, appears to be unlimited in many lower plants,
such as the Diatomaces, Oscillatoriee, &c.; at all events, any
other mode of: propagation has been either rarely or not at all
discovered in them; in other cases, however, and especially in the
Desmidiacese (see Ralfs’ “British Desmidica,” 5) this division is
confined within definite limits. After a series of divisions have
taken place, this process ceases, and the formation of spores
begins. ‘ ;

‘Among the plants possessing a thallus composed of numerous
cells, the development of single cells or groups of cells into inde-
pendent plants occurs chiefly in the Lichens, where very frequently
the layer composed of globular cells breaks up, by the cells fall-
ing apart into the form of powder (gonidia, lagerkevme), either

THE VEGETABLE CELL. 105

at particular points or all over the thallus, these cells falling upon
foreign bodies and becoming developed into new plants, if they
find a favourable station. But this phenomenon is to be regarded
as more or less a result of disease, for the normal development of
the thallus is interfered with by it, and if the formation of goni-
dia occurs to a great extent, is perfectly arrested ; thus this mode
of multiplication of Lichens becomes the more inconsiderable in
proportion to that by spores, the more favourable the station to
the normal development of the plant, and vice versd. The same
phenomenon is met with again in the leaves of the J ungerman-
nies, which frequently break up more or less completely into
pulverulent masses of isolated cells ; but it has not yet been ob-
served whether these are capable of further development into new
plants. But the formation of the so-called gemme occurs nor-
mally in many frondescent Liverworts, especially in Lunularia,
Marchantia, and Blasia. These structures are developed, in
hollow receptacles of various form, from a stalked cell, which is
converted by repeated subdivision into a cellular nodule, which
becomes detached, readily strikes root, and grows up into a new
plant. (See Mirbel, “ Recherch. s. l. Marchantia polymorpha.’)

Far more important, or perhaps merely better known, through
the masterly researches of W. P. Schimper (“Rech. Anatom. et
Morph. s. t. Mousses”), than in the Liverworts, is the part played
by multiplication through independent growth of single cells in
the Mosses, for almost every cell of the surface of these plants is
capable of conversion by repeated division into a cellular nodule,
which grows up into a leafy stem, whence is explained the extra-
ordinary diffusion of these plants, even of such species as never
bear fruit in particular localities. Schimper observed this process
on the rootlets of the Mosses, partly directly, partly after they had
become converted into a green structure composed of confervoid
filaments, resembling the proembryo; he found the same pro-
embryo-like structure grow out from the leaf-cells of many species,
(¢. g., Orthotrichum, Lyellit), and confirmed what Kiitzing had
already seen, that even the cells of torn leaves will produce simi-
lar growths under favourable circumstances. In particular cases
also, compound organs (the leaves of Miniwm palustre, M. androgy-
num, the antheridia of Tetraphis pellucida, &.) are developed.
into tuberous structures, spontaneously separating.

From the fact that the cells of different parts of the Mosses are ca-
pable of becoming developed into a bud or a proembryonal confer-
void structure producing a bud, it follows that in these plants, not-
withstanding their already rather complex structure, the subordi-
nation of the individual cell to the purposes of the whole is still but
small, and that the individual life even here readily acquires the
preponderance. But whether in the higher plants the individual
cell is still capable of coming forth independently in an analagous
manner and giving rise to the formation of a bud by development

106 ANATOMY AND PHYSIOLOGY OF

of acellular mass in its interior, or whether a complete group of cells
must co-operate from the very beginning for the formation of the
bud, we shall not be able to decide until we shall have traced back
the normal development of buds to their first origin. If, however,
it should be the case that the formation of a bud starts originally
from a single cell, this is still incapable, in the higher plants, of
forming a bud, when it is separated from the rest of the plant be-
fore it has produced a new individual and this has grown up to a
certain point of development, at the expense of nutriment produced
by other cells. Therefore in all the more highly organized plants
only organs of considerable size, composed of numerous cells and
containing a certain amount of assimilated nutriment, are capable
of laying down the foundation of a new plant.

I have explained above, the doctrine that a branched plant is
composed of as many individuals as it possesses ramifications.
Taken strictly, this is not absolutely true, for a perfect plant pos-
sesses not only an ascending axis, clothed with leaves, but a de-
scending axis, a root. In many plants (im all leafy Cryptogamia,
and in the Monocotyledons), even the primary axis is imperfect,
for merely the ascending portion of it exists, while a primary
descending axis is wanting, and is replaced by secondary axes
which shoot out from the lateral surfaces of the stem. The same
incompleteness exists in every branch, it consists merely of an
ascending axis, therefore corresponds simply to half a plant, as also
each ramification of the root represents the corresponding half of
a complete plant.

Since, however, the individual parts of a plant very generally
possess the power of producing that part of a complete plant in
which they are deficient, when either a sufficient supply of nutri-
ment has been stored up in their interior to last, or the requisite
sustenance is still conveyed to them by the parent plant, until the
completion is attained and they can prepare their own food inde-
pendently, there exists, as a rule, little difficulty in producing
4 new individual furnished with all necessary organs, from a single
part of a plant. This is most readily effected with an ascending
axis, since, on the whole, this is very prone to produce radical
fibres from its lateral surfaces, and thus to become placed in a con-
dition to sustain itself independently. It is more difficult to raise
a new plant from a detached descending axis, since such a root 1s
obliged to produce a leaf-bud, from which the future stem has to
grow up; a reproduction which in general is much less readily
effected than the formation of lateral roots from an ascending axis.
Finally even a detached leaf may give origin to the formation of
a new plant; in this case it must form both root and leaf-bud,
to which, generally speaking, the leaves have but very slight
tendency.

The readiness with which both descending and ascending axes
are formed at places where they do not make their appearance in

THE VEGETABLE CHLL. 107

the natural course of vegetation, varies extremely in different
plants, while at the same time we are unable to find a reason for
this variation in the organization of the particular species of
plants ; in many species, for instance in the rooting of Cactez,
Willows, &c., this development takes place so readily, that it can
be counted on with the greatest certainty, while in others the
development of the wanting organs, for example, of roots and still
more of leaf-buds in Pinus, never or but very rarely occurs. In
general the formation of the said organs takes place the more
readily the richer the detached part is in parenchymatous cellular
tissue, and the more assimilated nutriment there exists deposited
in it, at the expense of which it may be sustained until the organ
necessary to make it a complete plant is formed; but this rule is
only valid for the extreme cases, and, mostly, we cannot say
what is the reason, they are readily or not all inclined to such
production.

In very many plants, the formation of buds, which grow up
into distinct plants, is a regular operation, independent of external
causes. These frequently separate spontaneously from the parent
in a rather rudimentary condition, and grow into independent
plants subsequently ; in other cases, such separation occurs after
the parent plant is dead and decayed, through particular ramifica-
tions of it remaining alive.

In the plants having a thallus, we meet with the formation of
shoots which have not the form of the ordinary branches, but in
which the formation of the parent plant is repeated. Thus, in
the Algze, new plants are not unfrequently produced, both from
the frond and from the disk-like base of this, or out of stolo-
niferous prolongations of it. In the Liverworts and Mosses it is
a very general condition for single branches, the so-called innova-
tions, to repeat the form of the main stem, and when this decays,
to appear as the stems of new plants. In the higher plants,
ramifications very frequently occur, deviating in form from the
ordinary leafy branches, and destined to serve for the multiplica-
tion of the plant. They present themselves either in abbreviated
and thickened forms (as bulbs and tubers), in which case they do
not generally produce roots of their own until detached from the
parent, or, on the contrary, they exhibit a predominant longitudi-
nal growth (as runners or stolons above or below the surface of
the ground), in which case, roots are developed, and they sustain
themselves independently before their separation from the parent.
The branches destined to the multiplication sometimes sprin
from the normal place, from the axis of a leaf (e.g., the bulbels
of Lilium tigrinum) ; sometimes they originate from abnormal
metamorphoses of flower-buds (the bulbels of the inflorescence. of
many species of Alliwm, the tubers of Polygonum viviparwm) ;
sometimes they break out, as the so-called adventitious buds,
from spots which do not normally bear buds. The latter occurs

a Oe a ie REG METER TN MM RA
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‘meee emer a
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108 ANATOMY AND PHYSIOLOGY OF

on the roots of a large number of trees (¢. g., Poplars, Wild Cherries,
Plums, &c.), as well as on the leaves of many plants (¢. g., As-
pidium bulbiferum, Malaxis paludosa, and Bryophyllum cali-
cmnum).

The pollarding of a plant frequently causes the development of
shoots. The formation of roots generally takes place readily
when the descending sap is arrested anywhere in its downward
course by cutting through the bark, especially when, at the same
time, light is excluded from the wounded spot, and this kept
moist. In this case, the roots break out in most plants from the
thickening which is formed at the upper border of the wound.
On the other hand, the plant is caused to form leaf-buds in un-
usual places when the whole of the leafy part is cut off; for then
leaf-buds are formed beneath the bark, both on the lower part of
the stem and on the roots, breaking through the bark, and grow-
ing up into stems. Most Dicotyledonous trees possess this power
until they have attained too great an age, but most of the Coni-
feree are devoid of it. This capability of forming leaf-buds is so
great in many plants, that every fragment of the root may be
used for raising new plants from it,—for example, in the horse-
radish, Maclura aurantiaca, &e.

It is most difficult to induce the formation of buds on the
leaves. Detached leaves have very great tendency to form roots,
when they are placed in moist earth ; they afford, under such cir-
cumstances, the peculiar example of a plant which fully exercises
the functions of nutrition, but is altogether incapable of growth.
Such rooted leaves sometimes attain an age far exceeding their
usual period of existence; thus Knight, for example, saw the
leaves of Mentha piperita, which he had caused to produce roots,
maintain themselves fresh for more than a year, and assume
almost the aspect of evergreen leaves (Knight, “ Selection from
the Physiol. Papers,” 270). Growth into a new plant is only
possible in such a rooted leaf when it developes a leaf-bud; in
general, this does not readily happen. There are plants, it is
true, as already mentioned, on the leaves of which leaf-buds are
regularly developed ; and a considerable number of plants have
been noticed, on which buds had formed accidentally, on par-
ticular leaves, still connected with the plant, e. g., Drosera, Por-
tulaca, Cardamine pratensis, Glechoma hederacea, &c.; but, on
the whole, these examples are rare. Buds are most readily formed
on detached leaves when these have a fleshy consistence; their
development has been observed in particular on the bulb scales of
Eucomis regia, Lilium candidum, Hyacinthus, Scilla mari-
tama, on the leaves of Ornithogalum thyrsoides, &c.; moreover,
not unfrequently on the leaves of different species of Crassula
and Aloé. Buds are formed much less readily than on such suc-
culent leaves, on leathery leaves,—for example, of Citrus, Aucuba,
Hoya carnosa, Ficus elastica, Theophrasta, &e., although these

THE VEGETABLE CELL. 109

strike root freely (See “ On some wnusual Cases of Bud-forma-
tion ;” Munter, “Observations on special Peculiarities on the
Mode of Multiplication of Plants by Buds,’—Bot. Zeit. 1845,
537, et seq).

A detached portion of a plant is not, however, merely capable
of producing the organs wanting to form a perfect plant, but it
is also in a condition to become blended with another plant, and
lead a common life with it, on which capability depend the
numerous garden operations which are known under the not very
apt name of “ennobling” (veredeln, grafting). The conjunction
of young, succulent parts, still in course of development, is a
necessary condition of this blending. This condition is very easily
fulfilled in Dicotyledonous plants, because there exists between the
bark and the wood a layer of elementary organs in course of de-
velopment, the so-called cambiwm, and thus there is little diffi-
culty in so uniting the two plants, that this layer, of both parts,
meets at least at one point. But in the Monocotyledons, in which
the vascular bundles lie scattered through the whole stem, and no
definite cambium layer exists, the conditions are far more unfa-
vourable. It is true, according to De Candolle’s account (“ Physiol.”
u. 787), the gardener Baumann, of Bollwiler, succeeded in grafting
Dracena ferrea on Dr. terminalis ; but the graft died after one
year. But the experiments of Caldrini (“ Ann. d. Sc. Nat.’ 3me
ser. vi. 131) on the grafting of Grasses, had a more favourable
result, for he succeeded in grafting even species of different genera,
é.g., Rice upon Panicum crus galli with success, a result which
is explained by the fact that, in the Grasses the lower part of the
internodes enclosed in the leaf-sheath remains for a long time
soft and succulent. A second necessary condition of the blending
of growth, is great similarity of the two plants ; they must not
only be nearly allied botanically, but have a great agreement in
the composition of the sap.

Observ. 1. The possibility of grafting plants upon one another is de-
termined, in general, by their systematic position, yet many anomalies
occur. While it is usual that different species of one genus can be grafted
upon one another, and in many cases it is even possible in species of
nearly-allied genera, as, for instance, Pears on Quinces, on Crategus Oxya-
cantha, or on Amelancher vulgaris, while Syringa vulgaris at least grows
to Fraxinus excelsior, to Phillyrea latifolia, Olea ewropea to Fraxinus (De
Candolle’s “ Physiol.” ii. 791) and Castanea vesca to Oaks 3; yet, on the con-
trary, In many cases an union, or at least the maintenance for a long
endurance of the graft, cannot be secured, in spite of far closer botanical
affinity, e, g., between Chesnuts and Beeches, or Apples and Pears. ; :

Observ. 2. ‘The propagation by division is in many cases of the highest
practical value. Although the case occurs here and there, that a parti-
cular branch of a plant disagrees from the rest of the branches of the speci-.
men in certain small peculiarities of growth, the colour of the leaves, the
doubleness of the. flowers, the character of the fruit, &c., possessing the

110 ANATOMY AND PHYSIOLOGY OF

properties of a special variety, yet this is an exception to the rule. Every
part detached from a plant retains this agreement after its separation, and |
thus propagation by division affords the means of multiplying certain
varieties which could not, or only with uncertainty, be propagated by
‘seed. Cases certainly do occur in grafted trees where the composition of
the sap of the stock exercises a certain influence upon the characters of the
fruit of the graft, but on the whole, this is an exception. (Gartner has
given a comparative account of the observations on this subject, in his
“ Eoperiments and Observ. on Hybridation” —«Versuchen und Beobacht. tib
du Bastardbildung,” 606.)

b. Propagation by Spores and Seeds.

Tn all vegetables which attain their full normal development,
the period of vegetation is succeeded by that of fructification,
whether, as in the lower plants, the same cells which in youth
executed the vegetative functions, in their subsequent period of
life become organs of fructification, or, special organs of fructifica-
tion become developed. :

Odserv. The universality of this proposition is truly only borne out by
analogy with the majority of plants, for in the present condition of our
knowledge we cannot determine whether all vegetables fructify. In many
lower plants we are still unacquainted with any fructification, either be-
cause they are really deficient in them, as may be possible for instance in
the Yeast-plant, or that we do not know all the stages of their develop-
ment. The latter is the case in many lower plants; the difficulty of study-
ing them is increased by the fact that a large number of forms have been
described as peculiar species, especially among the Algz, which are only
earlier stages of development, and in many cases abnormal examples pro-
duced by unfavourable external conditions of plants frequently belonging
to totally different families.

The organ destined for a germ may always be traced back to
an origin from a single cell. When this cell, at the epoch of its
separation from the parent plant, contains no rudiment of a new
plant, but only an organizable fluid, or, in rarer cases, a few
secondary cells firmly blended with its membrane, and this cell,
after its separation from the parent plant, under the influence of
external circumstances favourable to the excitement of vegetation,
grows up directly into a new plant through expansion of its mem-
brane and production of new cells in its interior, this is called a
spore (spora, keimkorn). The formation of spores takes place
without fertilization, and plants which are propagated by spores
are termed Cryptogamia or Exembryonate.

When, on the other hand, the propagative cell (as embryo-sac)
forms part of a compound organ, and through previous impreg-
nation, produces in its interior the rudiments of a perfect plant,
furnished with stem and root (the embryo, kevm), and this becomes
detached with the enveloping parts formed by the further deve-

THE VEGETARLE CELL. _ 11]

lopment of the ovule, from the parent-plant, these envelopes to-:
gether with the embryo, are collectively termed the seed, and the
plants which bear seeds, Phanerogamia or Embryonate.

Observ. As will appear below, all the plants bearing spores are not
unisexual, but the impregnation in them stands in a totally different rela-
tion to the production of the new plant, from what it does in the Phane-
rogamia. In the latter, the formation of the embryo is the immediate
result of the impregnation ; when this does not take place, the seed
cannot germinate. In the Cryptogamia, on the contrary, which have an
impregnative process, neither the cell which forms the spore, nor the
spore itself become impregnated, but this is formed and becomes capable
of germination without a previous impregnation, and impregnating organs
are found, sooner or later, upon a germ-plant, or pro-embryo, growing from
the spore, upon the action of which organs depends the development of
the yet imperfect plant into a complete vegetable.

a. PROPAGATION BY SPORES.
a. Propagation of Thallophytes.

There is considerable variation in the modes of development of
the spores in the different groups of Cryptogamous plants. It
will not be without interest to take a brief glance at the principal
modifications.

In the Fungi we are above all struck by the production of an
enormous number of spores, so that in proportion to the great;
mass formed by the spores, and in the higher Fungi in proportion
to the large sporangium, the vegetative part of those plants, the
thallus, composed of loosely-connected filaments, and in most cases
devoid of any definite outline, exhibits an inconsiderable deve-
lopment.

In the lowest forms of Fungi, the Coniomycetes and Hypho-
mycetes, the formation of the spores, notwithstanding the innu-
merable shapes under which these plants present themselves, is
extremely simple, their production depending on a breaking-up
of the fructifying part of the Fungus into its constituent cells, or
into granules composed of several cells closely connected together ;
whence Léveillé says, correctly, that the Fungus consists, in its
simplest form, of a simple or cellular filament terminating in a
spore. When we come to the Mucorimew, we already find an
advance, for here, as in Ascophora, the extremity of the filament
expands into a vesicular cell, in the cavity of which a mass of
spores are formed by free cell-formation, A similar origin of the
spores is met with also in the higher forms of Fungi, in which,
however, the single cell producing the spores no longer constitutes
the entire organ of fructification, but large sporangia appear
under the most varied forms, wherein the parent-cells of the
spores are collected together in a definite layer, which sometimes
lines the cavity of the sporangium, as in the Gasteromycetes,

: as ~ - oar = ae, =
aes - . F Fades ™ 3 ; . =
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ae ee

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i
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Tie ANATOMY AND PHYSIOLOGY OF

sometimes forms a globular nucleus imbedded inthe substance of
the sporangium, as in the Pyrenomycetes, and sometimes appears
as a membrane lying free upon the outer surface of the sporan-
gium, as in Discomycetes and Hymenomycetes. In the higher
Fungi, the number of spores formed in a parent-cell is definite,
and we meet at once here that fixed numerical relation, which
remains the same in the formation of the spores of the Crypto-
gamia and of the pollen-grains of the Phanerogamia throughout
the whole Vegetable Kingdom, according to which, usually four,
more rarely eight or sixteen, spores or pollen-grains are formed in
a parent-cell, while the number may also sink on the other side
to two or one. Among the Fungi, four spores are formed in
the majority of cases (in the Hymenomycetes), sometimes only
two or one in a cell; in a few groups, as in the Tuberacecee and
Discomycetes, the number rises to eight (Léveillé, “Rech. s. Vhy-
men, d. Champign.”—Ann. d. se. nat. sec. ser. viii. 321; Corda
“Tcones Fungorum”’).

In regard to the form of the parent-cells, two modifications
occur. In the Pyrenomycetes, Discomycetes, and Tuberacee, they
appear as longish utricles (asci), in the cavity of which the spores
are developed by free cell-formation, after a previous production
of a nucleus, and then frequently (¢. g., Peziza ) each spore again
divides by a septum into two, sometimes even into more, cells. In
the Lycoperdacee and Hymenomycetes, on the contrary, four (in
rare cases only two, or one) protrusions of the wall of the parent-
cell are formed, each of which becomes the seat of the production
of aspore. These parent-cells are called basidia.

From the small size of the spores of most Fungi, it is not de-
cided whether the cell-membrane of the spore secretes a special
layer upon its outer surface in all cases (a kind of cuticle). Ina
great number this may be easily perceived ; like the outer coat of
pollen-grains, it is frequently covered with reticularly connected
ridges, little spines, &c. In germination, the coat of the Spore ex-
tends itself into a filament, which in the minute mildew-like Fungi
is capable of growing on into a perfect plant. Whether this pro-
duction of a new Fungus from a single spore occurs also in the
higher Fungi, or whether the filaments which grow forth from a
number of spores germinating side by side, must become com-
bined into a common tissue, has yet to be decided by observation.
The latter is at all events a common process, (See Ehrenberg’s
“ De mycetogenest, Nov. Act. Nat. Cur.” x. p.1, 161.)

In the Lichens the fructification of many Fungi (Pezizece and
Spheerraceee) is repeated most exactly. In the interior of the
thallus is formed a gelatinous nucleus of elongated cells, converg-
ing towards the central point, and embedded in an abundance of
intercellular substance. A portion of these cells become tubular
(asct or thecw) and produce the spores. In the naked-fruited
Lichens the thallus opens above the nucleus, and the latter spreads

THE VEGETABLE CELL. He

out into a more or less flat disk (the thecal layer) ; in the covered-
fruited, it remains enclosed in the thallus. In each of the parent-
cells eight spores are formed by free cell formation, and in very
many cases these form two, four or a greater number of secondary
cells in their interior. Very few observations have been made on
the germination of these spores. According to Holle (“ Zur Ent.
wickelungsg. von Borrera ciliaris.”’—On the development of B.
ciliaris, Diss. 1848, Gottingen), the secondary cells break through
the primary spore cell as filaments, and are con-
verted into cells outside the spore. According to
Meyer’s account (“ Nebenstunden mein. Beschaftig-
ung.” 175), the outer membrane of the spore is not
torn, and when a number of Spores germinate side
by side, the filaments into which they grow out be-
come blended together, and contribute jointly to the
formation of a new plant.

According to the observations of Tulasne (“I’In-
stitut,’ No 849), the inner spore-coat, both of simple
and compound spores, grows out into one or more
filaments, which soon ramify and acquire septa,
and whose short interlacing branches form little
cushions, upon which little colourless cells accumu-
late, and in which the green cells forming the rudi-
ments of the cortical layer of the new plant, make
their appearance.

We meet with a far greater complication of phe-
nomena when we look towards the spores of the Aloe,
even though here no co-operation of two sexes occurs,
This latter may indeed seem doubtful in a number
of Algee, in which a so-called copulation occurs, but
a more minute examination of this process shews |
that it bears no analogy to sexual reproduction.
This conjugation presents itself most distinctly in the
so-called Conjugate (the genera—Zygnema, fig. 49, ‘two cets of zy.
—Tyndaridea, Mougeotia, Staurocarpus, &c.), in uf cone
which it was observed first by Vaucher. The fila- crite eae
ments of these Confervee lie parallel, side by side, of the connecting

° : branch ; 0, con-
or bent in a “lZ-Zage manner towards each other, necting branch ; ¢,
and send out from their cell-walls towards the Pr
the nearest cell of the neighbouring filament, a blunt branch (a), '
which grows together with a similar and corresponding branch of
the other cell coming to meet it, upon which the partition in the
cross-branch (6) becomes absorbed, and the solid matter of the
contents of both cells becomes balled together into a mass in the
cavity of one of them, or in the connecting branch, this mass ac-
quiring a cellulose membrane, and in this way being converted
into a spore ee Tie following circumstances tel] against this
process being considered ag an act of impregnation. The contents

T

Fig. 49.

a

114 ANATOMY AND PHYSIOLOGY OF

of the two cells are exactly similar; sometimes all the cells of
one filament take away the contents of the cells of the other;
sometimes this happens only to a part of the cells, while the rest
empty themselves into the cells of the second filament ; and some-
times spores are formed in cells which have not copulated, all
this taking place without any definite rule.

Copulation has recently been discovered in many uni-cellular
Alges, in particular by Morren in Closteriwm (“Ann. d. Se. nat. see.
sér.” v. 257), by Ralf, in the Desmidiacess, and by Thwaites (“Ann.
of Nat. Hist.” xx. 9, 343) in the Diatomaceze. Remarkable as the
whole process of copulation is, its product is, in many respects,
enigmatical in no less degree. In the copulation of uni-cellular
Algee, two new individuals are generally formed; thus there is no
increase connected with this mode of propagation, but frequently
only one new individual is formed, and thus is presented the
strange phenomenon of a propagation resulting in a diminution
of the number of individuals, since the copulating individuals die.
In the Diatomaces, moreover, the individuals produced by copu-
lation are much larger than their parents. In the majority of.
copulating Algee, particularly in the Desmidiacese and Zygnemec,*
the spore produced from the union of the contents of the two cells
has not yet been seen to germinate, and it is not improbable that
it ought to be regarded, not as a spore, but as a sporangium, that
is to say, as a cell, the contents of which become developed into
numbers of germs (See Agardh, “Ann., d. Sc. nat. sec. Sér” vi. 197;
Hassall, “ Brit. Fresh-water Algo,” 24; Ralfs, “Desmidiew,” 10).

In by far the greater number of the Algz, the spores are not
formed by copulation, but in single cells, either, as in the lower
forms, in the vegetative cells towards the close of their existence,

or in special fructification cells.
__ The spores of a very large number of Algze, either before their
exit from the parent-cell, but principally in the period just succeed-
ing the emission, exhibit a movement, which is often very rapid.
These movements have not unfrequently been taken for animal,
voluntary motions, and have given origin to the most fabulous
conceptions concerning the transformation of animals into plants.
We owe the first extensive and accurate observations on these
moving spores to the younger Agardh (“dAmn. d. Se. nat. sec. S&r.”
vi. 193), who called them Zoospores. According to his researches,
they occur in the Nostochincee, Oscillatcria, Conserve, Conjugate,
Lictocarpcw, Ulwacce, and Siphonee. The following is his account
of their development. During the later periods of the growth of
the cells, the chlorophyll, which in the young cells of these plants
forms a homogeneous mass, becomes transformed into globules,
which towards the close of the cell’s life assume a spherical shape,
become detached from the wall of the cells and balled together in

* Erroneous in regard to Zynemez, -sce Vaucher, Meyer, and, more

recently, Pringsheim. Flora, Aug. 1852.—A. HI.

THE VEGETABLE CELL. 115

a globular lump in the middle. A “ swarming ” now begins to be
evident in this mass, the granules become isolated, and swim
about the cavity of the cell. A papilliform protuberance is after-
wards produced from the cell-wall, which tears at its apex, and
the spores making their way out by this orifice swim about in the
surrounding water. By degrees they begin to withdraw towards
the darkest part of the water, become attached to any solid body,
and begin to germinate, by an expansion of their membrane.
Agardh observed a transparent process (beak, Schnabel) at that
end of these spores which always went first in the movements,
But the true organ, on which this movement depends, is not this
beak, which itself ig motionless, but, as Thuret frst shewed
(“dan. d. Se. nat. sec. Sér.” xix. 266), there exist at the brighter
coloured end of the Spore, cilize of various lengths moving rapidly,
and by their vibrations causing the motion of the whole spore.
The number of these cilia differs in different genera. Thuret
found in Conferva glomerata (see tab. 1, 23, 24,) and rivularis,
two cilize on each spore, in Chetophora elegans four, on the spores
of Prolifera a circle of very humerous ciliz, (see tab. 1, 19—22,
which represent the spore (19) and its first stages of develop-
ment, after Thuret) ; subsequently (“Ann. d. Se. nat. 3ine, Sér.”
iu. 274) he made known that the spores of Hctocarpus have two,
those of Ulva and Lnteromorpha four cilis. . These observations
obtained full confirmation by others, especially by Fresenius
(“Zur Controv. ib. die Verwandl. von Infus. in Algen), and by
Alex. Braun (repeated by Siebold, “Ann. d. Se. nat. 3me. Sé.
xi 151). The opinion that these Spores possess animal life during
the period of their movement, and become plants at the moment
of germination, does not, however, depend merely on a confusion
of their movements with the voluntary motion of animals, but
derives an apparent confirmation from the fact that in very many
cases each of these spores contains a red spot (according to Nageli
a red oil-drop), which was taken for an eye by Ehrenberg and
others. Even before Thuret had made known his observations
upon the organs of motion of the zoospores, Unger (“Die Pflanze
im Momente der Thier- erdung”’) had published very minute —
observations upon the formation and motion of the very large
spores of Vaucheria. In Vaucheria, the single granules of chlo.
rophyll are not developed into minute spores furnished with a few
cilize, but the entire mass of chlorophyll of the terminal joint of a
filament, or of globular protuberances seated upon lateral branches,
after being separated from the contents of the rest of the fibre
by a septum, becomes balled together into one common spore,
which makes its way out by a slit in the cell-membrane and ex-
hibits rapid advancing and twisting movement. It is covered
all over with countless very short ciliz. The whole of the forma-
tion of the spore occurs early in the morning, its exit from the
parent-cell usually takes place about 8 A.M., and after its motion
I 2

116 ANATOMY AND PHYSIOLOGY OF

has endured for half-an-hour, or at most two hours, it comes to
rest, the outer coat covered with ciliz, disappears very rapidly (by
decomposition ?) and germination commences by the coat of the
Spore growing out into a filament.

Observ.—These observations first demonstrated the existence of ciliz
in the Vegetable Kingdom. It may be distinctly seen in Vaucheria
that they do not belong to the cell-membrane (spore coat), but to a mem-
brane clothing this. What the corresponding condition is in the zoospores,
is as yet unexplained, since a membrane enveloping the whole spore has
not yet been observed in these. Perhaps this may arise solely from the
_ small size of the spores and the tenuity of their coating membrane, per-
haps, however, the coat only exists locally around the beak and the points
of insertion of the cilie. Mettenius, indeed (“Beitrdge zur. Botamnk,” i. 34),
assures us that the ciliz are in connexion with the contents of the spores,
but he has not offered sufficient evidence of this. When we compare these
motions with the ciliary phenomena of animal cells ,and with the motions
of the seminal filaments of the higher Cryptogamia, no doubt can remain
that the movements of the cilize are the cause and not the effect of the
movement of the spore, as Nigeli (“Unicellular Alga,” 22) believed; an
opinion against which V. Siebold has already declared. The action of
poisonous substances, such as alcohol, opium, and iodine, immediately
arrests the motion.

Tt appears possible for the formation of zoospores to originate
from one single granule of chlorophyll, while in other cases, where
only one or few spores are developed in a cell, (¢. 9. Draparnal-
dia, Chatophora), perhaps larger sections of the mass of chloro-
phyll, or even the primordial utricle, by becoming constricted into
Separate segments, are the parts concerned in the formation of
the spores. The actual conversion into a spore is not accurately
known in its intimate processes, but must consist essentially in
the formation of a cellulose membrane around the chlorophyll
granules. It has already been remarked that in Vaucheria the
whole mass of chlorophyll of a cell becomes coated with a mem-
brane. Intermediate forms between these two extremes are met
with, thus Saulier (“Ann. d. Se. nat. 8me. Sér.” vii. 157) found
in the genus Derbesia, very closely allied to Vaucheria, that
neither the entire mass of chlorophyll collected into one spore, nor
did its grains remain isolated, but separate groups, each com-
posed of hundreds of grains of chlorophyll, became gathered up
into globular masses, acquired a membranous coat and formed a
short beak and a circle of cilize upon the surface.* Unger (“Lin-
need.” 1843, 129) observed a perfectly analogous formation of
the spores of Achlya prolifera, which, according to Thuret (“A nn.

* See further on this subject, Thuret, “Ann. des. Sc. nat. 3 Ser.” tom.
xiv. and xvi.; Cohn on Hamatococcus, Nova. Acta. vol. xxii, and on
Stephanosphera, “ Annals of Nat. Hist.” Oct. and Nov. 1852.—A. Braun.
“Ueb. die Verijungung,” Leipzig 1851. The active zoospores have no
cellulose membrane when first set free.—A. H.

THE VEGETABLE CELL. 117

d. Se. nat. 3me Sér.” iii. 274), likewise possess a circle of very
numerous cilize. .

Whether, as Agardh assumed, the power of motion in the spores
of the lower, and the want of it in those of the higher Aloze (the
Ceramiew, Floridew, and Fucacew) warrants a rigid division of
these plants into two sections, appears very doubtful, for accord-
ing to Decaisne and Thuret (“ Ann. d. Se. nat. 83me Sér.” tii. 10)
not only do the spores of the Fucacese present the same coat
covered with short ciliz as those of Vaucheria, which, however,
either from the size or some other cause are motionless, but there
also occur in the Fucaceze small moving spores bearing two ciliz,
enclosed in special cells, sometimes on the same plants that produce
the spores, sometimes on distinct specimens. The said observers,
indeed, have not recognized them as spores, but interpreted them
as seminal filaments, but they have not the least resemblance +o
these, while they agree with the zoospores in form and in the pre-
sence of a red point, the so-called eye. It is truly a remarkable
circumstance that one plant should bear two kinds of Spores, dif-
ferently formed, but the same occurs again as an universal rule in
the Ceramiee and Floridew, for these plants bear not only the
generally recognized spores, and gemma testifying their nature
as such by generation, which originate, like pollen-grains, in a
parent-cell dividing into four chambers (the so-called ¢etra-
spores), but other spores also, which are not produced in fours in
a parent-cell, and are contained in variable numbers in fructifica-
tions of the most diverse shapes (capsula, glomeruli, favella, &c.).
The spores of this second kind germinate, as Agardh has shewn,
like the tetraspores, their membrane extending itself on one side
into a root-like prolongation, on the other into a filament which
divides into cells, and grows up into a plant,

Decaisne and Thuret observed a most peculiar circumstance in
the spores of many Fucoides ; namely, the spores had not com-
pleted their development at the time of their maturation and de-
tachment from the parent plant, for, after this, commenced a divi-
sion into the proper germinating spores (in Fucus serratus and

esiculosus into eight, in F. nodosus into four, in F. canalicu-
lutws into two secondary spores).

Martins thought he had found, in the spores of Fucus, that the
separate spores did not grow up into new plants, but as in the
Fungi, a number of germinating spores became conjoined to form
one common plant. This has been sufficiently refuted by Agardh,
Decaisne, and Thuret. The spores of the Fucoidese germinate like
those of all other Algw, by expansion of their internal coat-on one
side, into a root-like fibre, on the other into a filament which
becomes subdivided into cells.

** Propagation of the Oryptogams having Stem and Leaves.

While in the three families of Cryptogamia possessing a thallus
(with the exception of the Charas, to be mentioned presently) all

= = ae 3

ww ee reer, Sen oe ape eee eee

wan eas

118 ANATOMY AND PHYSIOLOGY OF

attempts to discover male organs lias proved the more vain the ©
further the investigation of these plants has advanced, in the more
highly organised families of Cryptogamia, on the contrary, in which
there exists separation of the organs of vegetation into stem and
leaf, the last few years have seen the discovery of convincing
proofs of the existence of two sexes,

In the last century, when Hedwig in particular devoted himself
to the investigation of the Cryptogamia, the idéa that two sexes
must exist in all Cryptogamous plants, was quite predominant;
and thus, often enough without a trace of consideration, the most
diverse parts were, from mere opinion, separated as male organs.
This brought the whole effort to discover impregnating organs
into discredit, and the opinion that all the Cryptogamia were de-
void of male organs, and developed their spores without previous
impregnation, became more and more diffused. It is true that
organs had been discovered in certain Cryptogamous families, espe-
cially the Charas and Mosses, which from the time of their appear-
ance, from their position, &c., stood in evident relation to the fruit :
but since no positive influence could be proved to be exerted by
them upon the young sporangia, their function as anthers was
denied ; although it was at the same time admitted they had a
certain analogy with them, whence they were, indeed, called an-
theridea. In more recent times, two circumstances seemed chiefly
to strengthen the earlier doubt which had been entertained as to
the function of the antheridia. My own researches, namely,
shewed that the spores of the higher Cryptogamia do not, as had
been previously supposed, exhibit a resemblance in respect to their
development and structure, to the seeds of the Phanerogamia, but
that the most perfect agreement exists between them and the
pollen-grains of the Phanerogamia. From this it necessarily, yet
strangely, appeared that organs of perfectly like structure fulfilled
the function of germs in one part of the Vegetable Kingdom and
in the other part constituted the male, impregnating organs ; but,
little as the formation of a pollen-grain depends upon an impregna-
tion, no one circumstance shewed itself in the development of the
spore, at all more resulting from the co-operation of an impreg-
nating organ. Still more doubtful did the theory of the impreg-
nation of the Cryptogamia necessarily become, when N ageli made
the discovery, in the Ferns, of antheridia in many respects resem-
bling those of the Mosses, which were not formed upon the full-
grown plant at the same time as the rudiments of the sporangia,
but occurred upon the germ-plant (pro-embryo), while the perfect
plant was devoid of them.

Under these circumstances, Schleiden seemed to be warranted
in characterizing the effort to discover impregnating organs in the
Cryptogamia, as a mania. But by good luck, certain men who
had this mania did not allow it to. lead them astray in their
researches, and as often happens, nature this time proved so rich

THE VEGETABLE CELL. 119

that, not indeed was what had been sought found, but instead of
this a series of conditions, the existence of which was previously
altogether unsuspected. The researches relating to this point are,
it is true, still far from their completion, since at the present
moment nothing more than a preliminary notice of isolated con-
clusions already arrived at can be given; but these, although isola-
ted, cause us to expect with certainty in this field.a series of the
most striking discoveries.

The Mosses have served for a very long period as the main
props of the view that two sexes and an impregnation occur in
in the higher Cryptogamia. Not only was attention naturally
called in these to the constant occurrence of the antheridia, and
their great development, but trustworthy experience, formerly of
Bruch, more recently of Schimper (“ Rech. s. l. Mousses.” 55) de-
monstrated that Mosses which have antheridia and the rudiments
of sporangia upon the same stem always bear fruit, while dicecious
Mosses never setfruit in localities where only female specimens grow.
No one has succeeded in making out the mode in which the anthe-
ridia act upon the rudimentary fruit; but the physiological fact.
just mentioned does not lose its force on that account.

A second family indicating the necessity of an impregnation, were
the Rhizocarpez, since numerous observations had shewn that the
large and small spores of these plants could not be separated
without preventing the former growing into newplants. Schleiden,
indeed, had extended his theory of the development of the embryo
from the pollen-tube to this family, and arranged them -with Phane-
rogamia. But nothing was gained by this, for, on the one hand,
Schleiden’s whole theory of impregnation proved a false beacon ;
on the other, Schleiden’s statements as to the Rhizocarpeze were
not confirmed, and this more particularly in the most essential
point, the mode of origin of the embryo.

Then unexpectedly appeared Count Leszcye-Suminski’s essay
on the development of Ferns (“Zur Entwicklungsgesch. der Farren-
kréuter,” 1848), the contents of which at first seemed fabulous, so
contradictory were they to all that was known of the organization
and development of plants. But a more minute study of this treatise
—a comparison of the author’s results with nature—soon shewed
that although he had been deceived in a few particulars, his ac-
count was far from being a creation of the fancy, and that his re-
searches had broken open a path to a long series of discoveries.

In all families of the leafy Cryptogamia (with the exception of
the Lycopediaceze*) antheridia have been discovered, exhibiting it
is true considerable variations of external form and structure in
the different families, but collectively agreeing in the circumstance
of developing in their interior very delicately-walled cells, at first
containing an amorphous substance coloured yellow by iodine, in
place of which, at the epoch of maturation of the antheridia, a deli-

* Now found in these also, see note further on.—A. H.

20 ANATOMY AND PHYSIOLOGY oF

cate filament presents itself, displaying several spiral convolutions,
thickened at one end and running off to a very fine point at the
other. The filaments manifest lively motions, exhibiting differences
according to the manner in which they are rolled up, in some cases
while still enclosed in the cells where they are developed, but
more particularly after they have emerged into the water from
antheridium, which opens when ripe. Thus, when the filament
is rolled up like a watch-spring, the motion is more or less rota-
tory, but if it is coiled over in the form of a cork-screw, the move-
ment is at the same time an advancing one. In these movements
the thin end of the fibre almost always goes first. Minute obser-
vation, which in many cases is very difficult, both from the rapi-
dity of the motion (which, however, is readily arrested by poisons),
and the great delicacy of the whole structure, shews that the
movements arise from extremely delicate and comparatively long
cilize, of which two are usually found at the thin end of the fila-
ment, and which only seem to occur in larger numbers in the
Ferns. The filament itself exhibits no independent motion, as
indeed, altogether, the kind of motion does not indicate any will.
The term seminal filaments has been not inaptly applied to these
filaments.

Observ. The first observation on the motion of the contents of the
antheridia was made by Schmidel (“ Icones plantarum,” 1762, 85) in Jun-
germanma pusilla. The imperfection of the microscopes of that period,
however, seems to have prevented his seeing the seminal filaments, and
he probably only observed the cells in which the filaments were enclosed.
The same seems to have been the case with the observations made by Fr.
Nees von Esenbeck (“/lora,” 1822, 1, 34) in the antheridia of Sphagnum.
He considered the moving bodies which he saw to be globular monads,
and did not doubt their animal nature. The spiral filaments themselves
were discovered by Unger in the Mosses and Liverworts (“ Ann. d. Se.
nat. 2, Ser.” xi, 257) ; in accordance with the then prevalent notions on
spermatozoa, he regarded them as animals, and applied to them the
name of Spirillum bryozoon. Recent years have scarcely added to hig
observations on the seminal filaments, more than the fact that two cilize
exist at the thin end of the filaments, which Unger had overlooked (De-
.caisne and Thuret, “Ann. d. Se. nat. 3, Ser.” iii 14). Plate 1, figs. 26—28.
Seminal filaments of Sphagnum ; fig. 26, represents two anther-cells with
the seminal filaments enclosed ; fig. 27, one of the latter seen from the
side (from Unger). To me the filaments appear to have the form which
I have represented in fig. 28.

The structure of the Moss-anthers is very simple. It consists of a
simple sac, with a wall composed of a single layer of cells, which, according
to Unger, are applied upon the outside of a large cell, while according to
Schimper they are enveloped on their outer sides by a continuous mem-
brane composed of intercellular substance. When mature, this coat is
torn at the apex, and the contents, now dissolved into a mucilaginous
fluid, issue from it.

The anthers of the Liverworts possess a structure completely analogous
to that in the Mosses (Gottsche, “ Act. dead. Nat. Cur.” xx. 1, 293),

THE VEGETABLE CELL. 121

only the wall of the sac, at all events in many species, is composed of two
layers of cells.:

The anthers of Chara, of which Fritzsche (“Ueber den Pollen,” 6) has given
the most accurate description, possess a highly complicated structure. Into
the globular cavity enclosed by the eight cells containing red-coloured gra-
nules, projects a flask-shaped cell, almost as far as the middle 3 from its
apex run out a mass of fine confervoid filaments, which are divided up
very closely into joints, and in each of the cells is: developed a seminal
filament. The existence of an ix-fusorial motion of these filaments was
observed by Bischoff (“ Cryptog Geir.” 1, 13) ; their exact form (plate 1,
fig. 25, from Thuret), and the two ciliz, by which they approximate closely
to seminal filaments of the Mosses, were first made out by Amici (whose
essay on this.subject has not been printed) and Thuret (“ Ann. d. Se. nat.
2 Ser.” xiv., 66).

In the Ferns the most different parts had long ago been interpreted,
without any judgment, as male organs, even the stomates of their leaves,
the annulus of their capsules, &., when N ageli (“ Zeitschr f. Wiss. Bot.”
1,168) made the unexpected discovery that antheridia containing mov-
ing seminal filaments, occur upon their pro-embryo. This was contrary to
all theory, yet as the observations of Thuret (“ Ann. d. Se. nat. 3 Ser.”
xi 5) and Leszeyc-Suminski shewed, nevertheless proved well founded.
The structure of the antheridia of these plants bears a considerable re-
semblance to that in the Mosses ; they are composed of a pedicellated
cell, in the cavity of which is formed a second cell, filled with the small
cellules containing the spiral filaments. The entire organ bursts at its
summit, and extrudes its mucilaginous contents enclosing the seminal
filaments. The latter are ribbon-like and flattened down, possessing,
according to Suminski (plate 1, fig. 29) about six, according to Thuret
numerous ciliz. Schacht (“ Linnea,” 1849, 7 38, &c.) agrees with the last
statement, and states that the cilie are attached upon the narrow curves,
and not on the thick end at the widest curve of the filaments,

Thuret found the same organ on the pro-embyro of the Equisetaces.

The last Cryptogamia on which the spiral filaments have been found
are the Rhizocarper.* Nigeli (“ Zeitschr f. Wiss. Botanth. iii 199) suc-
ceeded in finding them in Pilularia. The pollen-grains (small spores)
undergo a change after they have been discharged from the anthers, by
the inner coat bursting the outer, and afterwards tearing, itself, to emit
minute cellules which are filled with mucilage and starch. In these
minute cells a vacant space is subsequently formed at one end, in which
appears a spiral filament, turning round and round, and leaving the cell
the thin end foremost. The same phenomena have been observed by
Mettenius in [soétes (“ Beitr. 2. Bot.” 1, 17).

Thus have antheridia and seminal filaments been found in all the leafy
Cryptogamia, with the exception of the Lycopodiacexe.t Whether semi-
nal filaments occur in any other of the Thallophytes besides the Charas,
remains tobe seen. It is true that N ageli (“Die neuer Algensysteme,” 186 ;
“ Zettsch. f- Wiss, Bot..” iti, 224; “ Bot. Zeit.” 1849, 572) has stated that
antheridia occur in the Florides, the essential parts of which’ consist of

* + Hofmeister (“Pruchtbildung, Keimung, &c., der Cryptogamen,” Leipz,
1851) has since shewn that the small spores of Selaginella produce seminal
filaments, exactly in the same way as those of Isoétes,—A. H.

122 ANATOMY AND PHYSIOLOGY OF

cells 1-900th of line in diameter, with a scarcely visible spiral filament
within ; but it may be permitted, considering the difficulty which such
minute size of the organ opposes to observation, to doubt, with Mette-
nius, whether there are really seminal filaments,*

The uniformity of the seminal filaments contained in the an-
theridia of the leafy Cryptogamia, leaves no doubt, in spite of the
difference of structure as above described, that these organs are
of the same physiological nature. The circumstance, however, that
these organs present themselves at such different stages of deve-
lopment of the plants, must appear in the highest degree surpris-
ing and indicative of altogether unlooked-for differences in the
propagation of these vegetables. From the study of the Phanero-
gamia, we are accustomed to regard the organs of fructification as
the last stage of vegetable development, since their formation puts
a period to any growth of the vegetative axis, and the maturation
of the seed frequently involves the death of the parent organism.
We meet with the same condition in the Mosses, in which the an-
theridia and the rudiments of the sporangia are developed at the
same time, the full development of the fruit succeeding the ripen-
ing of the anthers. In the Ferns, on the contrary, the condition
is diametrically reversed. The development of the sporangia fol-
lows the usual law, but the formation of the antheridia takes place
upon the pro-embryo after the spores have germinated, never to
be repeated in the plant growing up from the pro-embryo. In the
Rhizocarpee, finally, the cells which enclose the seminal filaments
are first developed after the pollen-grains (small spores) have been
shed; they are as it were dicscious plants, in which only the fe-
male plant arrives at perfect development, the male being arrested
at the stage of a germinating pollen-grain, which only produces
seminal cells, and then dies.

Before I pass to the consideration of the female organs of fructi-
fication of these plants, it will be necessary to speak of the spores
and their development.

I have already indicated that the spores of the higher Crypto-
gamia agree completely with the pollen-grains of the Phanero-
gamia in regard to their development and structure. Not only
in a portion of the Cryptogamic families, namely in the Hquise-
tacese, Ferns, and Lycopodiacez, does the sporangium fully agree
with the theca of an anther in morphological respects (“ Morph.
Betracht. des Sporang. d. m. Geftss. verseh Kryptog.,”—Mohl
“ Verm Schrift,” 94), but the development of the four spores in a
parent-cell, and their structure, as has been more minutely pointed
out above, are completely in agreement with the development and

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—A. H. .

THE VEGETABLE CELL. 123

structure of the pollen-grains. Just as the latter are developed in
the anther without the co-operation of another organ, does this occur
also in the spores. In certain Cryptogamia (the Rhizocarpese and
Lycopodiaceze) we find the peculiar condition, that spores of two
kinds are developed simultaneously, ina wholly analogous manner
in parent-cells, in capsular receptacles of two kinds, the spores
larger and smaller, possessing exactly the same structure, except
that one kind are larger and have a tougher outer coat. But in
the Rhizocarpez, only the larger exercise the function of spores,
the smaller, as above stated, developing the cells which contain
seminal filaments; in the Lycopodiacee, on the contrary, both
kinds of spores produce plants.*

The germination of the spores is as little dependent as their
origin upon a previous impregnation derived from the antheridia,
unless perhaps this be the case with the Charas, in which the

Fig. 50.

Za
Pro-embryo of Funaria hygrometrica (according to Young pro-embryo of Pteris ser
Schimper) a, rudiment of a bud ; b, a young stem ; ¢, first rulata according to Leszeyc-Su-
development of the pro-embryo from the spore; d, deve- minski.
lopment further advanced.
relation of the antheridia to germination is altogether unknown.
In germination (except in Chara) the spore does not grow at
once into a plant like the parent, but is first developed into a
thallus-like, cellular structure, totally devoid of vascular bundles,
. the so-called pro-embryo, which appears under very different forms
in different plants of these tribes. In the Mosses (fig. 50) it pos-
sesses the form of a branched Conferva, in the Ferns (fig. 51) the
shape of a cordate leaflet not unlike a frondose Liverwort, in the

* Anerror. See page 121, note; also Report on the Reproduction
of the higher Cryptogamia, by A. Henfrey. “Zrans. Brit. Assoc.” 1851.
—A. H.

124 ANATOMY AND PHYSIOLOGY OF

Equisetaceze of an irregular mass of cells divided into many lobes.
The development of the pro-embryo is extremely simple in these
plants. The spore-coat (fig. 50 ¢. d.) becomes expanded in germi-
nation, bursts through the outer membrane of the spore, sends out
hair-like prolongations serving as rootlets on one side, and becomes
prolonged on the other into the form of a cylindrical cell, which
becoming divided by septa into a number of cells, and so on by
continued growth and cell-multiplication, is gradually developed
into the perfect pro-embryo. In these plants no part of the spore
seems to be pre-determined for the production of the said parts, but
every point of it to be capable of the development described ac-
cording to the position in which it may be placed.

But the germination of the large spores of Lycopodium, Mar-
silea, Pilularia, Salvinia, and Isoétes, is more complicated ; in
them not only is that part of the spore, which by the contiguity
of the four cells in each parent-cell, has acquired a more or legs
evidently three-sided pyramidal form, the only germinal point of
it, but the pro-embryo is developed up to a certain stage in the
interior of the spores, and issues from the rent in the outer spore-"
coat, as an already parenchymatous structure, of different form in
different genera.

The pro-embryo of the Mosses is capable of transforming one or
more of the cells seated upon its various ramifications, immedi-
ately into buds, which grow up into leafy stems, so that here we
have the peculiar condition of one spore giving rise to the deve-
lopment of a number of plants.

The pro-embryos of Ferns, Rhizospermes, Equisetaceze, and Lyco-
podiacege, on the contrary, are incapable of the immediate produe-
tion of leaf-buds, and produce upon the uppermost layer of cells,
one, or mostly a number of peculiarly-formed organs, which, fol-
lowing the example of Leszcyc-Suminski, are called ovules, from
which organs, but not until after an impregnation by the anther-
idia, which discharge their contents at the same time, the future
plant grows out under the form of a bud ; when this impregnation
fails, the pro-embryo remains infertile.

In the Ferns and Equisetacese the pro-embryo produces the an-
theridia with the ovules, at the same epoch ; in the Rhizocarpes,
on the contrary, the parent plant which furnishes the large spores,
forms at the same time smaller, for the purpose of producing an-
theridia, and these small spores, as already mentioned, in like man-
ner exhibit a kind of germination, the product of which consists
not of an embryo, but of antheridial cells. In the Lycopodiacese
the conditions are still obscure. (See note p. 121.)

The ovule consists of a large cell belonging to the tissue of the -
pro-embryo, with four cells or rows of cells overlapping it on the
outer surface of the pro-embryo, and leaving an intercellular pas-
sage between them leading down from the open air to that cell.

Count Leszcyc-Suminski, the discoverer of these ovules in the

THE VEGETABLE CELL, 125

Ferns, observed the penetration of the spiral filaments into the
canal just referred to. His idea that he saw the lower part of
a spiral filament become transformed into the embryo, is doubtless
the result of a mistake, readily to be pardoned in such difficult
investigations, which does not damage the discovery we owe to
him. There can be no doubt that in the rest of the plants under
consideration, the spiral filaments are the bearers of the impreg-
nating substance, since in the Rhizocarpez, the spores which are
allowed to germinate separately from the small spores producing
the spiral filaments, are capable indeed of forming a pro-embryo,
but not of producing a plant from the ovules of this.

The plant, which is developed in the lower cell of the ovule, is
organically connected with the pro-embryo; it is a bud growing
up from it, so that the leafy stem thence produced has no primary
descending axis. (An error; see p. 137—A. H.)

According to Hofmeister’s researches, the relation of the anthe-
ridia of the Mosses to the rest of the plant is again different. It
has long been known, as already mentioned, that the rudiment of
the fruit of these plants remains undeveloped when no antheridia
are produced. This is explained by Hofmeister’s investigations ;
according to these, the rudiment of the fruit of the Moss (the
so-called archegoniwm) greatly resembles the ovules of the
Ferns, since underneath the so-called style, lies a large cell, which
by subdivision is converted into a cellular body, growing down-
wards and becoming blended with the stem at the one end, and
becoming prolonged upwards, and developed into the sporangium
at the other. So that while in the Ferns, &, the spore only
forms the pro-embryo without impregnation, and the impregnation
is necessary for the development of a leaf-bud, which grows up
into the leafy stem forming the sporangia, the spore of the Mosses
forms the pro-embryo and the leafy stem without impregnation, and
this operation only causes the development of the spore-producing
part of the plant (see W. Hofmeister, “ib d. Fruchtbild. und
Kemung d. hoh. Kryptog.’—Bot. Zeit. 1849, 793; Mettenius,
“Beitr. z. Bot.” 1. (Also Hofmeister, “Fruchtbildung, Keimung, &e.,
der Cryptogamen,” 4to, Leipzig, 1851; and Henfrey’s Report in
the Transactions of the British Association, 1851; and Memoir
on the “Reproduction of the Higher Cryptogamia,” &e.—“Ann. of
Nat. History,” sec. 2. vol. ix., 1852—A. H.)

6. PROPAGATION BY SEEDS.

Proceeding to the theory of the impregnation and the formation
of the embryo in the Phanerogamia, we arrive upon ground which
has been levelled by the researches of the last ten years. In no
part of our science has careful investigation, penetrating with un-
tiring patience into ultimate details, yielded more brilliant results,
yet in no other part have the hardly-earned facts been go violently
opposed, the conclusions, safely established, being even still contin-
ually called in question onthe strength of superficial investigations,

126 ANATOMY AND PHYSIOLOGY OF

Observ. As the minute exposition of the historical development of the
theory of the sexes of plants would occupy far too large a space, an indi-
cation of the main points must suffice. Although the cultivation of
many moneecious and diccious plants might have led, even in ancient

- times, to the idea that plants were furnished with sexual organs of two
kinds, this truth was not recognized until towards the end of the 17th
century. First announced in England by Grew, Ray, and others, this
theory obtained its first scientific establishment from R. J. Camerarius of
Tubingen (“De sexu plantarum epistola,” 1694); but it was Linnzeus more
especially who securely established this new theory by his researches, and
gave it universal diffusion by the preponderating influence he exercised in
Botany, and by the displacement of all earlier systems by his Sexual System.
When, finally, Kélreuter, succeeded by a longer series of experiments in
demonstrating the possibility of producing Hybrids in the Vegetable King-
dom (“Vorlaust. Nachricht einig. d. Gleschlecht d. Pflanzen betreff, Versuche.”
1761—1766), the theory of the sexuality of plants was as firmly establish-
ed as it could be without a knowledge of the changes which the pollen-
grains undergo upon the stigma and the processes occurring in the
ovule. The last century did not essentially advance further in reference
to this point. The excellent researches of Malpighi, if not forgotten or
misunderstood, were at all events not completed ; as to the structure and
characters of the pollen and as to its relations to the stigma, numerous in-
correct observations were published. With this imperfect knowledge of
the processes occurring in the interior of the ovule, it might easily be
thought possible that fertile seeds should be perfected, at all events, in
particular cages, without the co-operation of the pollen, and a number
of observations were made known, partly in favour of such exceptional
cases, and partly with the object of refuting the entire theory of the sexes
of plants ; thus Spallanzani and others asserted that female specimens of
Hemp, Spinage, é&ec., had borne fertile seeds ; Henschel believed that
road-dust, powdered charcoal, sulphur, &¢., might be substituted for the
pollen ; Schultz stated, as the result of his observations, that the pollen
need not necessarily come in contact with the stigma, but might impreg-
nate from a distance by an awra seminalis ; and Lecoq thought he had
found that fertile seed might be developed without application of pollen
to the stigma in monocarpic, but not in polycarpic, plants. The doubts
thus excited were set at rest for ever by the brilliant discovery of
Amici, that the pollen-grains germinate upon the stigma and that their
internal coat grows down in the form of a tube through the style
into the ovary, and comes into connection with the ovule (1823— -
1830); a discovery to which Gleichen had already come very near,
but had not properly followed out. The universality of this process
has indeed been denied, but day by day the opposition becomes more
completely silenced. Parallel with the researches on the structure of
the pollen and its relation to the stigma, went the investigations on the
ovule and the origin of the embryo, which had been taken up again from
the last-mentioned period by Treviranus, and subsequently carried out
further by Rob. Brown, Brongniart, Mirbel, Schleiden, Hofmeister and
others. In the midst of this new development of the theory of impregna-
tion, not the sexuality, but the respective import of the sexual organs,
was unexpectedly called in question, by Schleiden stating that he had disco-

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THE VEGETABLE CELL. 127

vered that the embryo was not the product of the ovule, but originated in
the tube growing into the ovule from the pollen-grain, whence the pollen-
grain was to be considered as the true ovule, the plants hitherto regarded
as male as the female, and vice versd. Here again it was Amici, who by
decisive observation solved the doubts arising out of this theory, and de-
monstrated the new doctrine to be false, a result which soon obtained full
confirmation from other investigations, especially from the extensive ob-
servations of Hofmeister and Tulasne.

* The Pollen.

As the development and structure of the pollen-grains have
already been spoken of in the account of the development of cells,
I shall confine myself here to a few remarks upon this organ.

The perfect pollen-grain consists of a cell, usually roundish. or
elliptical (elongated into a filament in Zostera), which, excepting
in certain water-plants, is coated on the outside by a membranous
layer, which owes its origin to a secretion, and, in particular cases,
is separable into two or three superincumbent layers. The outer-
most membrane, corresponding to a cuticle, is mostly rather tough,
uniform, or covered with granules, spinules, projecting linear and
often reticulated ridges, mostly coloured, and the seat of a more or
less abundant secretion of a viscid oil. The internal coat is a co-
lourless, uniform, soft, and extensible cellulose membrane. Its ca-
vity is filled with a viscid fluid, rich in protoplasm, sometimes
transparent, sometimes rendered opake by granules swimming in it
(fovilla). In the pollen of very many plants the outer coat forms
one or more regularly arranged folds inwards, in which it very
frequently exhibits pore-like, thinner places at one or more points;
in like manner, very many pollen-grains without the folds, have
similar pore-like places, varying from one to a very considerable
number, which when large are closed by a piece of the outer coat
serving as a cover.

When a pollen-grain comes in contact with water, it powerfully
absorbs this, through the endosmose excited by its dense fluid con-
tents, swells up and tears in many places, in consequence of the
strong expansion its membranes undergo through the absorption
of water. If the pollen-grain opposes the pressure of the absorbed
water through the toughness of its membrane, the inner membrane
is driven out, in such pollen-grain as have pore-like places in their
outer coat, in the form of a papilla, which often extends into a
rather long, cylindrical tube (e. g., in Dipsaceze, Geraniaceze, Cu-
cubitacese). As this phenomenon occurs in pollen-grains which have
been long dried, and in fact very suddenly, it can be attributed
only to mechanical expansion dependent on the peculiar structure
of the parts referred to, and not to an actual growth.

But when fresh, living pollen comes in contact with water which
contains organic substance in solution, e. g., with the stigmatic
secretion of the fluid of the nectaries of flowers, its inner coat
grows out, in one or more places, in the form of a tube, the length

128 ANATOMY AND PHYSIOLOGY OF

of which, by true growth depending on nutrition, often comes to
exceed the diameter of the pollen-grain a hundred times.

Observ. The granules of the fovilla have given rise to many false asser-
tions ; Ad. Brongniart, in particular, thought he had discovered that they
agreed in form and size in each species of plant, and had an independent
motion, whence he compared them with the spermatozoa of animals
(“ Ann. d. Se. nat.” xii. 40., xv. 381). Rob. Brown also (“A Brief Account
of Microscopic Observ. on the Particles contained in the Pollen of Plants,”
1828), although he discovered at the very time the molecular motion of
the fovilla-granules, was of opinion that a change of form might be perceived
in the larger granules (which he called particles). Against these state-
ments I was compelled to declare most positively (“ Ueber d. pollen,” 30),
I neither found a definite form and size of the granules in the pollen of
any given plant, nor could detect in them movement of any other charac-
ter than that of the molecular movement ; to similar results came Fritzsche
(“Ueb. d. pollen,” 24), who shewed that these very grains which had been as-
serted by Brongniart and Brown to change their form, were nothing but
starch grains, while other seeming granules were drops of oils ; the ma-
jority of the smaller granules may, however, as in all protoplasm, consist
of proteine compounds. These granules are invisible in many fresh pol-
lens, since the fluid in which they swim has the same refractive power as
the granules, whence such pollen-grains are as transparent as glass lenses;
when their fovilla is mixed with water the granules at once become
visible.

The fovilla seems always to be at rest in the pollen-grain when
it comes from the anther, unless Zostera (Fritzsche 1. c. 56 ) forms
an exception. But when the pollen-grain has germinated upon
the stigma, the fovilla exhibits a circulation similar to that of the
protoplasm of Vallisneria and Chara, flowing downwards in a
broad stream into the pollen-tube, and back upwards on the oppo-
site side.

Observ. This phenomenon was first seen by Amici in Portulaca (“ Ann.
d. Sc. nat.” ii. 68), subsequently in other plants, especially in Gourds and
in Hibiscus syriacus (“ Ann. d. Sc. nat.” xxi. 329). Since it appears that
no other observer (except Schleiden, who saw the circulation in pollen-
tubes which had been developed in nectar) has been able to see this pheno-
menon, it may be permitted me to mention how the observation is to be
made. In Portulaca it is not difficult, if a freshly-impregnated stigma is
exposed to bright sunshine for a few minutes, the style then removed
from the flower with forceps, and the stigma upon which the pollen tubes
are very quickly formed, is observed dry, with a power of at least 200
diameters. In the Gourd (for as Amici told me himself, his observations
were made on this plant, which in Italian is Zwcca, and not on Yucea as it
is stated in all books) a layer must be sliced from a stigma powdered
with pollen an hour previously, and this slice pressed moderately between
two glass plates, to heighten its transparency.

In the development of a filament from the internal coat of the pollen,
we meet with a new analogy between the pollen-grain and the spores of
Cryptogamous plants, since we have evidently before us a process of germi-

~

THE VEGETABLE CELL. 129

nation resembling that we observe in the spore. But the pollen-grain
does not seem to be capable of a further development, under favourable
external circumstances, into a plant like the parent, yet Reisseck and
Karsten observed that under certain circumstances, e. g., when pollen-grains
were enclosed in hollow stems like that of the Dahlia, their inner coat was
capable of an abnormal development, and of conversion into lower forms
of Fungi.
** The Ovule.

The Ovule (ovulum, Hichen),—of late years called by the ad-

herents of Schleiden’s theory of impregnation the seed-bud (samen-
knospe) or gemmule, consists essentially of a parenchymatous
papilliform growth from the ovary, of the so-
called nucleus (ei-herne, nucleus ovuli fig. 52,
a), the tercine of Mirbel, in which towards the
epoch of impregnation one cell becomes more
enlarged, displacing a greater or smaller portion
of the parenchyma of the nucleus and forming
the embryo-sac (the guintine of Mirbel).

In far the greater number of cases the ovule
does not stand still at this first stage, in which
it consists merely of a naked nucleus, but un-
dergoes, before impregnation, a more or less
extensive series of changes, which relate partly transverse Section of
to the formation of enveloping, membranes, en- Finvyose? o Lane cont

closing the nucleus, and partly to alterations of of the Ovule (primine) ;
5 d, Outer Coat (secwn-

form dependent upon curvatures of the different dine); ¢, Micropyle; ¥f,

Chal 2 Funi S.
parts 5 f the ovule. halaza ; g, Funiculus

The coats of the ovule originate in this way: at a variable dis-
tance from the summit of the nucleus, an annular collar of cells
makes its appearance, growing into a thicker or thinner coat which
gradually rises up round the nucleus and contracts over its apex
leaving only a little orifice, the micropyle (ei-munde, fig. 52, e).
In the majority of ovules, a second coat (fig. 52, cd) is formed in the
same way, lower down than the first (fig. 52, e) which it encloses.
That part of the ovule where the simple or double coat is connect-
ed with the base of the nucleus (fig. 52, f), is named. the chalaza,
and when beneath this there exists a cylindrical portion, it is
called the funiculus (nabelstrang, fig. 52, g).

Observ. Since the changes of form, which the ovules of most plants un-
dergo in the course of their development, exercise no influence upon their
impregnation, I shall be content to indicate briefly their principal modifi-
cations. When the axis of the ovule remains straight, as it is always at
first, so that the micropyle is situated at the summit of the ovule, and the
chalaza coincides with the hilum, both lying at the extremity of the ovule
opposite the micropyle, the ovule is called orthotropous or atropous (gerad-
léiuyfig). When the ovule curves over on the end of the funiculus, so that
the upper part of the latter comes to lie parallel with one side of the
ovule and grows together with it, the ovule is named anatropous (gegenliu-
jig). In an ovule of this kind the chalaza lies at the geometrical summit of

K

130 ANATOMY AND PHYSIOLOGY OF

the whole, the funiculus coherent with the ovule forms a ridge running
along one side (the raphe), the hilum (the point of insertion of the fanicu-
lus) Ties beside the micr opyle, at the lower end of the ovule, and the axis
of the nucleus is straight. But when the nucleus itself is curved to one
side by an unequl growth of its two sides ; so that the micropyle comes
to lie beside the chalaza at the base of the ovule, and the highest point of
the ovule is formed by the curved side-wall, the ovule is called campylo-
tropous (krummldufig).

Although not difficult of investigation, the knowledge of the structure
of the ovule advanced very slowly. An excellent foundation was laid by
Malpighi ; but it was Robert Brown, who first opened the path to
further progress, by his description of the ovule of Kingia. The researches
of Brongniart and Mirbel, which latter clearly unfolded the mode of ori-
gin of the different forms of the ovule from the orthotropous, but gave a
very incorrect account of the coats of the ovule, were followed by the ob-
servations of Fritzsche, who cleared up the latter point, and the extensive
investigations of Schleiden, who, through a large quantity of detailed re-
search, earned very great credit by making known the different modifica-
tions of the structure,—the varying number of the coats,—the universal
occurrence of the embryo-sac,—the origin of this from a cell, &c. Hof-
meister (“ D. Lntsteh. d. Hmbryo der Phanerog.”) traced back the earliest
— stages of development of the ovule further than any previous observer, and
found (in the Orchidez) that it takes its origin from a single cell of the
epidermis of the placenta, this cell dividing by a cross section into two
cells, one lying above the other, the upper of which, is converted by further
subdivision into the cortical layer of the nucleus, and the lower, into the
central cellular cord, the uppermost cell of which becomes the embryo-sac.

According to the ordinary view, the ovule is to be considered as a bud,
the axis of which is metamorphosed into the funiculus and nucleus, the
leaves into the coats of the ovule. The order in which the coats are de-
veloped, might certainly be fairly urged against this opinion ; but I can-
not question its correctness, since it is not unfrequent in malformed ovaries,
for the ovules to grow out into leafy shoots.

With regard to the physiological import of impregnation, it is perfectly a
matter of indifference whether the ovule is regarded as a product of the
carpellary leaves, according to the theory eee by Robert Brown
and De Candolle, or it is award: with Schleiden, Endlicher, and Unger,
and others, that the placenta is always an axial structure. It would lead
me too far to relate the reasons for and against these two theories ; each of
which is true of a portion of the Vegetable Kingdom, but neither of
which, and especially the latter, can be exclusively applied to all Beers
without coming into contradiction to the clearest facts.

Detailed researches on the structure of the ovule are to be met with,
especially in the works of Mirbel (“ Rech. sur la structure et developement
de lovule végétale,” Ann. des Sc. nat. xvii), Schleiden (4 Geb. die. Bildung
des Eichens” Act. nat. cur. xix. p. 1. “ Grundz der wiss. Botanik”), Hof-
meister (“Die Entstehung des Hmbryo der Phanerog.” and Tulasne (“ Ann.
des Se. nat 3me Sér,” xii.).

* * The Origin of the Embryo.

The irotscty of the ovule by the pollen i 18 an indispensable
condition to the origin of an embryo in it. It is true that the

THE VEGETABLE CELL. 131

ovary may grow up into a fruit, and the ovule into a seed nor-
mally formed on the exterior, without this, but the latter is in-
capable of germination, because it contains no embryo. In the
naked-seeded Phanerogamia (the Cycadese and Conifere), the
pollen falls upon the freely-exposed ovule, and impregnates it
immediately ; in the rest of the Phanerogamia, in which the
ovules are enclosed in an ovary, the impregnation is effected
through the medium of the pistil, with the stigma of which the
pollen must come in contact.

In the majority of plants, the ovary is not perfectly closed
above, its cavity being prolonged upward into a very narrow canal,
which runs through the substance of the style ; or if the borders
of the carpellary leaf where this forms the style, are not blended
together, it has the form of a groove running on the inside of the
style. The cellular tissue which forms the wall of this canal, is
distinguished from the rest of the tissue of the style by softness
and transparency, and frequently also by the absence of colour. At
the epoch of the perfect development of the pistil, there exudes
among its cells (which are usually much elongated, but may also
be roundish) a mucilaginous fluid, which so loosens the connection
of the cells, that they may be readily separated, and through the
expansion caused by the excreted fluid, they frequently quite close
up the canal of the style. This cellular tissue, which, after
Ad. Brongniart, is called the conducting tissue, appears at the
upper orifice of the canal, where it is frequently enlarged into a
large globular or lobulated body, free to the external air, and this
constitutes the stigma. The cells forming the stigma are ordi-
narily less elongated than those lying in the interior of the style,
and are often more firmly blended together. The outermost layer
of them does not form a continuous, smooth epidermis, but its
cells are usually in the form of papille of variable length ; and
papille of this kind present themselves along the whole of the
canal of the style, upon the surface of the conducting tissue. At
the opposite extremity of the canal, the conducting tissue stretches
into the cavity of the ovary, and here, in general, runs on its wall
to the points of insertion of the ovules, where it appears in very
different forms, varying according to the structure of the ovary,
the number and position of the ovules, &c.; sometimes covering
* the many-ovuled placenta as a broad layer ; sometimes running,
in the form of a narrow strip, to a single ovule; sometimes pro-
jecting, in a conical shape, into the cavity of the ovary, and
coming into direct contact with the micropyle of an ovule, Wc.
The conducting tissue is by no means to be regarded as a special
organ, but consists of a modification of the tissue of the carpellary
leaf, occurring at particular parts,—usually of its upper surface,
where this forms the canal of the style. In other cases, however,
this modification of the tissue may go out through the substance
of the carpellary leaf to its posterior surface, as in the Asclepiade,

K 2

132 ANATOMY AND PHYSIOLOGY OF

in which this forms but a very small part of the colossal style, or
in Lomatogonium, where the coherent borders of the carpellary
leaves consist of stigmatic substance along the whole of the ovary.
The pistil is incapable of fertilization, until after the secretion
of the above-mentioned viscid fluid upon the stigma, for though
the pollen-grains indeed adhere to the stigma from being more or
less glutinous, they cannot be any further affected. But as soon
as this secretion has appeared, the germination of the pollen-
grains commences, often in-a few minutes, in any case in a few
hours. The inner coat breaks through the outer in the form of a
cylindrical tube, which applies itself to the stigmatic papille
(sometimes, as in Matthiola annua, penetrates into them), grows
downwards among them, and penetrates between the.cells of the
conducting tissue. Ordinarily only one tube is emitted from each
grain, but in those grains which possess several pore-like points
on their outer coat, and in which the portion of the inner coat
situated beneath those places always becomes developed into a tube, ©
one grain not unfrequently produces several tubes, the number
having been seen by Amici to amount to 20—30. The pollen-tubes
make their way, by continuous growth at their ends, through the
conducting tissue of the style into the ovary, attaining, in long-
styled plants, like Cactus grandiflorus, for instance, a length
which may exceed the diameter of the pollen-grain several
thousand times. This considerable length alone, but still more the
circumstance that the wall of the pollen-tube is often exceedingly
thin in proportion to its cavity, shews that its formation does not
depend upon mechanical extension of the pollen-membrane, but
on a growth, the requisite nutriment for which is drawn from the
viscidfluid poured out among the cells of the conducting tissue.
The rate at which the growth takes place varies very much
in different plants, and is not subject to any universal rule. The
first result of it is an attachment of the pollen-grain to the stigma,
so that it can no longer be readily wiped off the latter. According
to Gartner, this often takes place in even half a minute, while, in
other cases, many hours may elapse (in Mirabilis and the Mal-
vacec, as many as 24—36). The growth of the pollen-tube down
the style likewise occupies very varied periods in different plants.
In many plants, several weeks pass before the pollen-tubes have
passed through a style only a few lines long, while in others,
even when the style is very long, a few hours suffice (¢.g., in
Cactus grandiflorus and Colchicum). After the pollen-tubes
have penetrated the stigma, the secretion of the latter ceases, and
its tissue begins to die away, while the lower part of the pollen-
tube is still in a growing condition. The fovilla passes down-
wards in proportion as the tubes are elongated, so that the pollen-
grains collapse on. the stigma soon after their application upon it.
The pollen-tubes being so long, the fovilla must certainly become
more and more considerably diluted by the absorbed fluid, yet it

THE VEGETABLE CELL. 133

seems always to become more or less granular and opake. The
pollen-tubes are distinguishable from the cells of the conducting
tissue, partly by their opake contents, and partly by their smaller
diameter (which is often very small, ¢.g.,in Orchis Morio about
1-180th of a millim, in Digitalis purpurea 1-166th, in Cheir-
—_anthus Cheiri 1-280th, in Capsella Bursa-pastoris 1-332).

Arrived in the ovary, the pollen-tubes, when not immediately
led to the mouths of the ovules by special arrangements of the
conducting tissue, creep in a mostly very serpentine course along
the placenta, among the ovules, and finally penetrate singly, or
several together, into the micropyle canals of the ovules.

Observ.. A considerable time elapsed from Amici’s first observation on
the emission of the pollen-tubes upon the stigma of Portulaca (1823),
before their further path to the ovule was detected ; for though Brong-
niart (1826) demonstrated, by numerous observations, that: the pollen-tubes
penetrated the conducting tissue, he thought he found that their lower
ends burst, and that their fovilla was conveyed to the ovules by the con-
ducting tissue. Amici (1830, “dun. d. Se. nat.” xxi. 329) discovered the
perfect course to the ovule, but even in 1832, Robert Brown was still in
doubt whether the tubes penetrating the ovules of the Orchidez were
pollen-tubes, or, more probably, tubes formed in the style, and to which
he applied the name of mucous tubes, a doubt which was completely
settled by Amici’s researches, as was also the opinion advanced by many
later observers, that this phenomenon does not occur in all the Phanero-
gamia :—shewn to be totally mistaken, by the extensive researches of

Schleiden, Hofmeister, &ec.

~~ Tt is one of the most puzzling phenomena existing, that the ends of the
pollen-tubes reach the micropyles of the ovules, the admission to which is °
not always very simple ; since this rencontre seems to be left to pure acci-~
dent, it might be conjectured that for this purpose a very large numbér
of pollen-tubes were necessary. Yet. such is not the case. It is true
that in the majority of plants, the number of pollen-tubes which are deve-
loped upon the stigma is very considerable, and we not unfrequently see
whole bundles of them penetrate the ovary, which is readily accounted
for by the vast number ofpollen-grains found in the flowers, a tolerable
proportion of which generally reach the stigma. Thus Kolreuter found
4863 pollen-grains in the flower Hibiscus Trionwm, and according to
Amici?s estimate the pollen-grains of an anther of Orchis Morto can fur-
nish 120,000: pollen-tubes. But the number of pollen-grains necessary
» for impregnation is by no means large. For example, in Kélreuter’s
_ | experiments on ibiseus Trionum, 50—60 pollen-grains sufficed to impreg-
| | nate all the ovules in the ovary (over 30) ; when fewer pollen-grains
} | were placed upon. the stigma the ovules were not all impregnated, for in-
‘| stance, by 25 pollen-grains only 10—16 ovules. In Mirabihs Jalapa and

longiflora one, or at most three, sufficed to impregnate the ovule.

Tt ig not necessary to the success of an impregnation that the pollen
should pass immediately from the anther to the stigma, for it seems to
remain capable of fertilizing for some days in all plants, while in some it
retains its power even for a year. Thus Kolreuter found thatthe pollen
“of Hibiscus Trionum kept fresh.-three days,,fhbat of Cheiranthus Cheiri,
fourteen days ; the pollen of Phenix dactylifera is said to be capable of

134 ANATOMY AND PHYSIOLOGY OF

being preserved for a year in the Hast ; and the same time has been
asserted for Cannabis, Zea, and Camellia, (See Girtner “ Befruchtung der
Gewachse,” 1, 146.) 5

In order to explain the course of the processes which go on in
the interior of the ovule, it will be necessary for me to return to
its structure. Towards the epoch of impregnation, the embryo-
sac has mostly become greatly enlarged in proportion to the other
parts. In many plants it i8 still enclosed in the interior of the
nucleus, so that its upper end, directed towards the micropyle, is
still covered by one or more layers of parenchymatous cells be-
longing to the nucleus. In other plants (for example in the Or-
chideze and Syngenesia), the embryo-sac (pl. 1, fig. 12, s ; 13, s) has
by this time wholly displaced the entire nucleus, or at least the
upper part of it Gn the Leguminose also the inner coat of the
ovule), and in certain cases, in particular in Santalum, has be-
come so much elongated that it projects freely out of the micro-
pyle. The pollen-tube which has penetrated into the micropyle
(pl. 1, fig. 14, p: 15, ».) in its further elongation, thus comes either
immediately in contact with the apex of the embryo-sac, or with the
layer of cells covering it ; in the latter case it penetrates between
these cells, and in this way likewise reaches the embryo-sac.

In the latter there is always a more or less abundant quantity
of protoplasm. In the later period, just before the pollen-tube
reaches the embryo-sac, a portion of the protoplasm becomes at-
tracted into the upper end, next the micropyle. In this proto-
plasm nuclei appear, usually to the number of three (pl. 1, fig. 12),
and give rise to the formation of as many cells (pl. 1, fig. 13, b ; 14),
which more or less completely fill up the upper part of the cavity
of the embryo-sac, and are termed the germinal vesicles (embryo-
blischen). The triple number, although usual, is not universal,
for in many plants (¢. g., Agrostemma Githago, according to Hof-
meister) only one germinal vesicle is formed, while in other cases,
as in Funckia coerulea, a larger number present themselves. One
of them also, as Hofmeister observed in Canna, may displace the
rest before impregnation through its predominating enlargement.
With these cells necessary for the origin of the embryo, a variable
number of other cells are also formed in other parts of the embryo-
sac (pl. 1, fig. 4, /'), chiefly in the end turned away from the mi-
cropyle, more rarely in the central region. But this cell-formation
is neither an universal phenomenon, nor does it stand in relation
to the impregnation.

When the pollen-tube has reached the upper part of the embryo-
sac, its growth is either immediately arrested, or it becomes elon-
gated a very little more, so that its obtuse, somewhat inflated end
usually penetrates laterally between the embryo-sac and the sur-
rounding cellular layer (pl. 1, fig. 14, 15), or, in rare cases (Narcis-
sus poeticus, according to Hofmeister ; Digitalis purpurea, and
Campanula Medium, according to Tulasne), introverts the mem-

THE VEGETABLE CELL. , - BD

brane of the embryo-sac for a short space. In extremely rare
cases (in Canna, according to Hofmeister), the pollen-tube breaks
- through the membrane of the embryo-sac, and thus comes imme-
diately in contact with the germinal vesicles. In the great majority
of cases, however, as already observed, the pollen-tube is separated
from the germinal vesicles by the membrane of the embryo-sac,
and frequently even, the point at which the end of the pollen-tube
«3 in contact with the embryo-sac, does not correspond exactly to
the point at which a germinal vesicle lies in the inside of the em-
bryo-sac (pl. 1, fig. 15). Therefore the only way in which a mate-
rial effect can be produced by the pollen-tube upon the germinal
vesicle, is by the fluid part of the fovilla transuding through the
membranes of the pollen-tube, the embryo-sac, and the germinal
vesicle. Itcannot be demonstrated that such a transudation does
take place, but it is in the highest degree probable, since it is in-
comprehensible how the impregnation of the germinal vesicle could
take place without it.

The pollen-tube begins to decay more or less rapidly after it
has reached the embryo-sac. Its growth is arrested, as before
noticed, and the fovilla contained in it undergoes a visible change
in its characters, acquiring a granular, half coagulated aspect ; the
pollen-tube itself is by this time evidently dead, and disappears
sooner or later (sometimes, however, not until the seed is ripe),
apparently through absorption.

Shortly after the meeting of the pollen-tube with the embryo-
sac, but only when this has occurred, the further development of
the germinal vesicle begins, this exhibiting a rapid growth, and.
usually displacing the two other germinal vesicles which ordi-
narily accompany it (pl. I, fig. 15) ; it is only in rare cases that
two or more of these vesicles simultaneously undergo enlargement.
The form which the growing germinal vesicle assumes 18 very un-
like in different plants; in many it grows but moderately in
the longitudinal direction, and thus becomes ovate; in others,
particularly in the Scrophularineze and Cruciferze, it grows into a
long cylinder, which frequently does not much exceed. the pollen-
tube in diameter, and exhibits a clavate expansion at its lower
extremity. During this enlargement, the protoplasm, which ori-
ginally filled up the germinal vesicle pretty uniformly, becomes
" principally collected at the lower end, after which cell-formation
by division commences (pL 1, fig. 15, 16). In this conversion of
the germinal vesicle into a cellular body, to which Hofmeister
applies the name of pro-embryo (vorkeim), abundance of modifica-
tions present themselves in different plants. In all cases the
vesicle first divides by a transverse wall into two cells, one above
the other (pl. 1, fig. 16, a, b.) ; the lower of these may at once be-
come converted. into a parenchymatous body (the embryo) by suc-
cessive subdivisions, as occurs in Monotropa, or, as is ordinarily
the case, the formation of the embryo does not commence until

136 ANATOMY AND PHYSIOLOGY OF

the pro-embryo has been changed into a compound cellular body
by successive subdivisions. In this process there may be forma-
tion merely of cross-walls, so as to change the pre-embryo into a
confervoid, jointed (pl. |, fig. 17, @; 18, a) frequently elongated
row of cells lying one above another (for example, in the Scro-
phularinese and Cruciferze), or the filamentous pro-embryo may
pretty early pass into a mass of cellular tissue by longitudinal
division of its cells (for instance, in Statice, Tropeolum, Zea, Fri-
tullaria, &¢.). Whichever takes place, the terminal cell of the
whole structure is sooner or later metamorphosed, by preponder-
ating growth and cell-division in different directions, into a cel-
lular structure, at first of globular form (pl. 1, fig. 17, b; 18, b),
which, the more fully it becomes developed, the more marked
contrast does it present to the other part of the pro-embryo turned
towards the micropyle end (called the suwspensor, Trager, or
Aufhingefaden). The ulterior development shews that this
mass of cells formed at the end of the pro-embryo is in the rudi-
ment of the embryo. It may persist, in plants with the so-called
“homogeneous embryo” (¢. g., in the Orchides and in M onotropa),
in the form of a globular or elliptical body, composed of a variable
number of cells (pl. 1, fig. 18) ; but usually the cotyledons shoot
out at the end turned away from the suspensor, a little below the
actual extremity (in the Monocotyledons in the form of a sheath-
ing leaf, in the Dicotyledons in the form of two opposite leaves,)
and after this the apex is developed into the terminal bud (plu-
mule, federchen).

In this way the embryo is always suspended in an inverted
direction, with the point of its stem downwards, in the embryo-
sac. Its radical extremity, as is evident from the mode of origin
of the embryo, is not free, but blended with the cells of the pro-
embryo; frequently it does not at once become clearly - distin-
guishable from the cells of the pro-embryo, but the line of de-
marcation becomes continually more definite with the advancing
development, since the cells of the embryo are always densely
filled with organic matters, while the cells of the suspensor usually
contain only a little opake sap, and are thus far more transparent
than those of the embryo, from which they are also frequently
distinguishable by much greater size. The further the develop-
ment of the embryo progresses, the more, in most cases, does vege-
tation cease in the cells of the suspensor, so that, if even, as in the
Orchideee, it still exibits a considerable growth during the deve-
lopment of the embryo, and exists when the seed is ripe, it at all
events forms but a dead, readily detachable appendage of the
radicle, upon the embryo of the ripe seed.

The origin of the embryo, which is formed out of a cell of the
pro-embryo, and not free in the cavity of the embryo-sac, bears oreat
resemblance to the formation of a bud, and especially to the for-
mation of the stem-producing buds developed on the pro-embryo of

ea oa mT a ae a ee

inn a hn BE

i
ne:
4

THE VEGETABLE CELL. 137

the Cryptogamia ; yet there exists an important distinction from
the formation of buds, in the fact that the lower end, connected
with the suspensor, becomes detached from this, and is capable of
further development, in consequence of which the primary axis of
the embryo can become elongated downwards, in germination, as
a tap-root, which is not the case in any buds, or in the young
stems of the Cryptogamia,* the axis of which is only capable of

prolongation upwards.

Observ. 1. Schleiden’s theory of the origin of the embryo (“ Hinige
Blicke auf die Entwickelungsgeschichte des veget. Organismus,” Wiegmann’s
“ Archiv.” 1837, 1, 289—“ Ueber die Bildung des Hichens und Entstehung
des Embryo” Act. acad. nat. Cur. v. XiX., p. 1.) is completely opposed to
the foregoing description of this process, since, according to him, the
embryo is not formed in the cavity of the embryo-sac, but in the lower
end of the pollen-tube, which introverts the wall of the embryo-sac, and
penetrates more or less deeply into the depression thus formed. If this \
theory were true, the germinal vesicle would not be an independent pro-
duct of the ovule, but of the clavate, expanded extremity of the pollen-tube,
and the suspensor would be the remainder of the latter, running into the
introverted portion of the embryo-sac. Tn the whole province of Vege-
table Physiology, seldom has a theory excited so much curiosity as this
theory of impregnation. No conviction was more firmly established than
that the pollen was the impregnating organ, hence the wonder that it
should be exactly the reverse. The confusion was great, for the theory
emanated from a man who shewed by his numerous and excellent re-
searches on the ovule, published at the same time, that he possessed an
acquaintance with his subject, such as few others had, and who in every
word expressed the conviction that the matter did occur as he asserted,
and that a mistake was out of the question. And others were not want-
ing to make known confirmatory observations (Wydler, “ Biblioth. Umi-
vers.” 1838, Oct. ; Géléznoff, “ Bot. Zeitung,” 1848, 841), or to support
the new doctrine on theoretical grounds, and teach it as a settled truth
(Endlicher and Unger, “ Grunds. der Botantk”). Tt is true that the old
notion had its defenders, but these maintained the fight a long time with
little success. Some who did not know how to use the microscope, thought,
nevertheless, that an opinion might be arrived at here, in which the thing
depended wholly and solely upon a fact to be determined by the micro-
scope, from other grounds, but such was utterly without value by itself ;
others, Meyen in particular (“ Physiologie,” iii), certainly had recourse to
the microscope, but were content with superficial observations, and thus
were not very fortunate in their intended refutation of the new theory,
for observations, in some of which not even the penetration of the pollen-
tube into the ovule, or the embryo-sac were seen, were not calculated to
drive an opponent like Schleiden out of the field, and the latter could
justly interpret some among such discordant observations as Meyen’s in
his own favour. It was Amici again who now for the second time came
forward with an observation marking an epoch in the theory of impregna-

Fe ager Raa” “3d ss

doh igo AS LE Ate

oe

* An error; the axis of the Ferns, &c., originates from a free embryonal
vesicle, and has an abortive descending axis, like the Monocotyledons.—
A. H.

128 ANATOMY AND PHYSIOLOGY OF

tion, and, by his researches on the impregnation of the Orchides (“ Sulla
jecundazione delle Orchidee,’—Giorn. Bot. Italian. Anno 2), made an end of
the new theory at one blow. Amici’s treatise was soon followed by a

confirmation of what he had seen by myself (“ Bot. Zeitung,” 1847, 465),
and others ; and these were quickly succeeded by the extensive researches
of Hofmeister (“ Die Hntstehung d. Embryo d. Phanerogamen”) and of
Tulasne (“ Ann. d. Se. nat. 3 Ser. xii), which contained a full confirmation
of the results obtained in the Orchidex, and demonstrated that the im-
pregnative process is the same in its essential circumstances throughout
a long series of Phanerogamia, so that this subject may be considered as
quite settled in its principal features.

Obs. 2. The so-called naked-seeded Dicotyledons (the Cycadex and
Conifer) present some very important differences from all other Phane-
gamia, in reference to the production of their embryo ; the circumstances
are unfortunately not all cleared up by the foregoing researches. The
differences depend, not so much upon the fact, that the pollen-grains fall
immediately upon the naked ovules in these plants, for nothing is essen-
tially altered by this, since the pollen-grains here germinate on the point
of the nucleus in the same way as in other plants, and are thus spared the
circuitous route which the pollen-tubes have to make through the con-
ducting tissue of the pistil. The distinctions lie in a great complication
of the structure of the ovule, and in the manifold deviations in the struc-
ture of the embryo.

In the Conifere, the nucleus is in great part displaced by the enlarge-
ment of the embryo-sac ; the latter becomes filled with cellular tissue,
out of which from three to six cells, arranged in a circle near the upper
end, become more considerably enlarged than the rest, and these consti-
tute what are called, by Robert Brown, the corpuscula,—by Mirbel and
Spach, the secondary embryo-sacs,—and also become filled up with cellular
tissue. The pollen-grains germinate on the point of the nucleus, and send
down their tubes through the upper part of it; and the slowness with
which this process takes place in many species is remarkable, for in Larix
europea, according to Géléznoff, the pollen-tubes do not emerge from the
granules till after thirty-five days ; and in Pinus sylvestris, Pineau states
that full a year passes before they grow down through the nucleus to the
embryo-sac, whereby evidently the impregnation is also postponed for this
long period. When the pollen-tubes have arrived at the embryo-sac, they
break through it, and through the cellular tissue lymg between its mem-
branes and the secondary embryo-sacs. The observations on their subse-
quent course are discordant. Pineau believed he had discovered that the
ends burst, and poured out the fovilla into the secondary embryo-sacs.
According to Géléznoff, the pollen-tubes would break through an inner
membrane immediately enclosing the fovilla, and grow into the secondary
embryo-sac. In like manner, there is an obscurity as to the origin of the
embryo. Apparently there originates in the secondary embryo-sacs,
from the cells already contained in them, a pro-embryo of most peculiar
form: in Pinus, the upper part of it is composed of a rosette of four to
five cells, to which an equal number are applied below, these extend them-
selves into a long filament, which again bears four cells at its extremity
constituting the rudiment of the embryo.. As the intermediate cells
grow down in the filamentous form, they break through the lower end of

THE VEGETABLE CELL. 39

the secondary embryo-sacs, grow onward in the cellular tissue lying in a
cavity of the primary embryo-sac, and push the embryo out of the secon-
dary embryo-sac. In this way are formed as many embryos as there are
secondary embryo-sacs ; but the four or five cells forming the thread-like
suspensor may separate from each other, and every one form a special
embryo. The embryo itself, moreover, exhibits a peculiar growth, for
while its cotyledonary end is composed of a connected, well-defined mass
of cells, its radical extremity is formed of a loose mass of cellular tissue,
which grows back on the suspensor, its cells only becoming more com-
pactly conjoined at a later period. Finally, in Thuja, a whole mass of such
suspensors are formed, which terminate in an embryo below, side by side,
* in one embryo-sac. The numerous embryos originating in one ovule seem
all to be equally capable of living, and are developed up toa certain point,
but then, from some unknown cause, all die away except one. (Robert
Brown, “On the Plurality and Development of Embryos in the Seeds of
the Conifercee,’—Ann. Nat. Hist. 1. Sér, xiii, 368 ; Mirbel and Spach,
“« Notes sur UV Embryogenie du Pinus Laricio,” &c.,“ Ann. des Se. nat.,”
2 Sér. xx. 257; Pineau, “Sur la Formation de VEmbryon chez les Com-
feres,’—Ann. des Se. nat. 3 Ser. xi, 83 ; Géléznoff, “Sur PEmbryogente du
Meleze, Bulletin, de la Societe de Natural. de M OSCOU,” xxii, “ Ann. des Se.
nat.” 3 Sér. xiv.)*

Observ. 3. If Schleiden’s theory of impregnation had proved true, it
would have furnished incontestible proof that no embryo can originate in
the ovule without application of pollen to the stigma. With the con-
firmation of the earlier view of the import of the pollen-grain, the doubt
again arises whether the geminal vesicle is not in isolated cases capable of
development into an embryo without impregnation. Improbable as such
an exception seems, when we look at the thousands of experiments which
declare the necessity of impregnation, the absolute impossibility of 1t can
the less be proved that undoubted cases of the possibility have been
shewn in the Animal Kingdom. The greater the accuracy in the observa-
tions, indeed, the more clear it became that the cases in which it was
supposed that the development of fertile seeds without impregnation had
- been observed, in the hemp, spinach, &c., arose from mistakes, but certain
cases still remain in which the problem has not yet been solved. In
reference to this, mention must particularly be made of the Euphorbia-
ceous plant, Celobogyne iicifolia, described by John Smith (“ Linn. Trans.”
xviii. 510), in which not a trace of anthers could be found, either by
Smith, or by Francis Bauer, Lindley, and others, and yet it bore perfect
seeds. Gasparrini likewise asserts (“Anm. d. Se. nat.,” 3 Sér. v. 206) that
the figs developed in summer never contain male flowers, and yet produce
seeds which contain an embryo.

c. THE CELL AS AN ORGAN OF MOTION.

Although plants in general appear completely fixed and motion-
less, a close examination leads to the detection of movements of

* Hofmeister has recently shewn that great analogy exists between
the Corpuscula and the Archegonia of the Cryptogamia. See Hofmeister,
“ Keimung, Entfaltung, &c., der hoher. Cryptogamen,” &e., Leipzig, 1851 ;
also reported in Henfrey “On the Reprod. of the Cryptogamia,” &e.—* Ann.
of Nat. History,” Ser, 2 ix. 1852.”

140 ANATOMY AND PHYSIOLOGY OF

the most diverse of their organs, which are sometimes dependent
on the influence of certain universally-diffused agents, such as
gravity and light, sometimes are excited by stimuli accidentally
affecting them, and sometimes occur independently without the
existence of any demonstrable external cause. Great as the simi-
larity to animal motion is in many of these movements, they are
always devoid of the character of volition, so that altogether no
more definite and profound distinction between plants and ani-
mals can be found, than the total want of voluntary motion in
the former and the presence of this same in the latter.

Observ:Unfortunately it is extremely difficult to make out, in many
cases, whether a motion is voluntary or not, yet repeated unprejudiced
observations will very rarely leave a doubt about it. In no other inves-
tigation does the observer need calm reflection in so high a degree as
here, for hundreds of examples shew how readily the imagination steps
in and leads to erroneous conclusions in the observation of the enigma-
tical movements of plants. Warning examples are furnished by ob-
servations on the “swarming” spores of Alge, on the Diatomacez,
Oscillatories, &c., in abundance; shewing how soon, when once the kind
of motion has been mistaken and these plants conceived to be animals, |
their entire structure has become misunderstood, and imaginary eyes,
intestines, feet, and other animal organs have been discovered, which’
more temperate observers have recognized as things differing as widely as
the poles.

In examining the movements of plants we must first of all
exclude those cases in which motion of an organ is caused by the
more or less complete drying up of different layers of it, producing
unequal contraction and thereby curling of the parts. The rapidity
of the motion produced in this way depends on the mechanical
conditions of structure; it may be slow or very rapid. The former
is the case when no external hinderance opposes the movement of:
the drying organ, the latter when the curving part is blended with -
other parts, so as to be hindered from following its contraction,
_ whereby a gradually increasing tension arises in it, the final re-

“sult of which is a rupture and a sudden relief of the stretched
part, like the recoil of a metal spring. In general, the layers of
an organ which contract most strongly in drying are those which
are composed of larger, thinner“walled, and more globular cells,
while a layer composed of thick-walled, small, and elongated
cells suffers less contraction, and therefore forms the convex side
of the curved organ.

Observ. Examples of these hygroscopic movements are of every-day
occurrence, and it will suffice to indicate a few of them. Among thege
are,—the contraction into a globe, which the ramified stems of man-
plants, such as Anastatica hierochontica, Lycopodium lepidophyllum, un-
dergo in drying ; the dehiscence of anthers, the bursting of most dry
fruit, the rupture of the outer seed-coat of Oxalis, the twisting of the
awhs of many grasses. In particular cases even isolated pieces of cel]-
wall exhibit movements of this kind, when their various layers differ

THE VEGETABLE CELL.

from one another in hygroscopical respects, ¢. g., im the elaters of Hquwise-
tum, the peristome of the Mosses, &c. The cause of these motions is
usually so conspicuous, and the proof that they result from desiccation so
readily shewn, since wetting the dried organ brings it back into its old
form, that the cause has but rarely been misconceived, and such motions
ascribed to a vital force, irritability, &c., in the way Purkinje so strangely
did, in regard to the opening of the anthers, in a special work (“ De
cellulis antherarum fibrosis,’ 1830).

Passing to the movements of living plants, we meet first, as
one of the most mysterious phenomena, the locomotion of many
lower aquatic Algze, the Diatomacez, Desmidiacese, and Oscilla-
torieze, which, on account of this, have been so frequently re-
garded as animals. In the Diatomaceze and Desmidiacez, the
motion consists of a slow waving backwards and forwards in the
direction of their longitudinal diameter, during which no change
of form, such as curvature or the like (which indeed would be im-
possible in the Diatomacez, on account of their siliceous lorica),
can be observed in the cell constituting the plant. Neither can
special organs of motion (such as cilize) be discovered, and Ehren-
berg’s idea that he detected a moveable foot, similar to that of
the Mollusca, must be attributed decidedly to erroneous observa-
tion.

The organic process upon which this motion depends is alto-
gether uninvestigated. Nageli (“Gattungen der evnzelliger
Algen,” 20) explains the motion by supposing, that in the absorp-
tion and excretion of fluid matters connected with the nutrient
processes of these plants, the attraction and repulsion of the fluids
are irregularly distributed over the portions of the surface, and
that these currents are so active as to overcome the resistance of
the water; but this explanation is devoid of any positive basis.
The external circumstances: in which the plants are placed have
influence over the motion so far, that when the little plants lie
hidden in mud, they rise up to its surface if the sun shines upon
it, and they bury themselves in the mud when its surface be-
comes dried up (Ralfs’s, “ British Desmidew,” 20).

The motion which presents itself in the Oscillatoriw is more
complicated, since not only does the entire plant move backwards
and forwards like a little rod, but a pendulous swinging of the
filaments to and fro occurs, together with a curvature in. a
spiral direction (See Kutzing, “ Phycol. Generalis,” 181 ; Frese-
nius, “Ueber Bau and Leben der Oscillarien,” in the Musewm Sen-
kenbergiamwm, iii. 284). - This curvature deserves our attention. in
a higher degree, that these plants are composed of a simple row of
flattened cells enclosed in a membranous sheath. Under these
circumstances, a curvature of the filament cannot depend (as in
the higher plants) upon a different relative contraction or expan-
sion of different cells lying. side by side, but must arise from a
different behaviour of the different lateral surfaces of the two side

a ANATOMY AND PHYSIOLOGY OF

walls of the individual cells, either the side becoming concave in
the motion undergoing abbreviation, or the opposite side expand-
ing. The locomotion of the entire filament is influenced in the
same way as that of the Diatomacez: and Desmidiaceze by illumi-
nation or drying up of the mud, and the movement from a dark
towards an illuminated place, is, in particular, very distinct (Du-
trochet, “ Mémoires,” i. 112).

Observ. This is, of course, not the place to enter into the much con-
tested question whether these beings are actually plants, and not rather
animals. The former is, as I at least believe, incontestibly proved by
Kiitzing (“Die Kieselschaaligen Bacillarien”), Ralts (“ British Desmidiee,”)
and others. But it deserves mention that the contraction into a spiral
form occurs not unfrequently in still higher degree than in the Oscilla-
toriew, in. most undoubted plants, namely, the Zygnemece (See Meyen,
“ Physiologie,” iii. 566).

Rapid advancing and retreating movements, like those the
lower Algze exhibit, are unknown in those organs of higher
plants, consisting of a single cell or row of cells, which might, in
reference to their structure, be compared with the plants above
referred to, yet we find in such simply constructed organs, pheno-
mena of curvation which are indeed most closely connected with
their growth, but may possibly be brought into connection, in
many respects, with the phenomena of motion. I include among
these the phenomenon, that many filiform cellular processes
grow in a definite direction, and attach themselves upon foreign
bodies.

The pollen-tubes are, above all, to be recalled to mind here,
curving, as they do, after their exit from the pollen-grain, to come
in contact with the hairs of the stigma, applying themselves upon
these, and penetrating into the conducting tissue of the style.
This phenomenon has often been compared with germination, and
correctly, for in that curvature, in the penetration of the pollen-
tube into the conducting tissue, we meet with the same pheno-
mena, only in a more simply organized part, as in the radicle of a
germinating plant. Still greater is the analogy with the radicles
of many Cryptogamia, whether these are protrusions of single cells,
as in many Conferve and in the Liverworts, or simple rows of cells,
as in the Mosses. In these capillary roots we find the same ten-
dency to grow downwards, and the same adherence to foreign
bodies. One might be inclined to seek the cause of this curvature
of the cells, and their adherence to foreign bodies, in a retardation
of the growth of those parts of the cell-membrane which come in
contact with the foreign bodies, behind that of the free parts of
the membrane. But it is possible that the conditions are far more
complicated. For if we compare these phenomena with the pro-
cesses which are presented to us in the compound organs of the
higher plants, we find in the movements of these capillary organs,
corresponding processes to those which, in the higher plants, are

Sees aR See TT
|
13
1

THE VEGETABLE CELL. 143

produced by not less than three causes (the influence of gravity,
light, and contact of solid bodies). Since, however, the external
influences upon which these movements depend, are as’ yet alto-
gether unexamined, and thus nothing but empty guesses can be
expressed regarding them, I feel that I ought to be content
with the indication, that even in the simple cell, phenomena of
motion occur which are comparable with those of the compound.
organs.

With regard to the motions of the parts of higher plants, so far
as they are connected with their growth, we are first struck by
the determinate directions of the root, the stem, and the leaves.
To no phenomenon have we been rendered—by having it daily
before our eyes—more indifferent, than to the definite direction
in which every part of a plant lies in reference to a perpendicular
line; and yet in the circumstance that the stem grows upwards,
the root downwards, and the leaf with its upper surface turned
towards the sky, we behold a series of the most wonderful pheno-
mena, the causal relations of which are unfortunately but too
little understood. These positions of the various organs seem
to us so natural, that it is only by the exceptions which occur in
many plants, and by the effort of a dis-arranged part to regain
its normal position, that our attention becomes attracted to the
fact that this position is the result of a series of mysterious pro-
cesses, which, though unnoticed, are ever active in the plant.

Experiments of the simplest kind, in particular such as were
made by Duhamel, have long since shewn that the earlier endea-
yours to explain the growth of the root downwards and of the
stem upwards, from the influence of the darkness and moisture
of the soil upon the root, and the brightness and dryness of the
air upon the stem, were mistaken, for under all circumstances, be
the position and the surrounding media of a germinating seed
what they may, whether this germinate in the earth, in air or in
water, in darkness or under the influence of light, the radicle and
the plumule will curve until they have acquired their normal
direction. The acuteness of Knight (“Phil. Trans.” 1806; “A
Selection from the Physiolog. Papers,” 124) obtained the first
success in demonstrating sure evidence of the connexion of this
phenomenon with the effect of a determinate force, of gravity, in
fact, by making seeds germinate on wheels rotating rapidly, under
which circumstances the radicles turned towards the periphery,
and the plumules towards the centre of the wheels. This experi-
ment was afterwards extended by Dutrochet to the leaves, where-
by he shewed that the leaves are also subject to the effect of
gravity, for these turned their lower faces towards the periphery
of the wheel (Dutrochet “ Mémoires,” ii. 54).

Observ. It is difficult to conceive how any naturalists could question
the value of the evidence furnished by this experiment, in which the

+

ot Sans sym asia oat sill ieee
inh nati, it gaSmscanaticl ae .

144 ANATOMY AND PHYSIOLOGY OF

effect of gravity was replaced by that of centrifugal force. But on the
other hand, the explanation given by Knight of the mode of action of
gravity in determining the direction of plants must be regarded as un-
successful. In this explanation Knight started from the different manner
in which the stem and roots grow longitudinally. The root, as is well
known, grows only at its extreme points. Knight believed that the half-
solidified substance of these points immediately followed the attraction of
gravitation, and curved downwards. With regard to the stem, on the
contrary, in which a series of internodes are undergoing elongation simul-
taneously, Knight thought that gravity could not act upon its already
formed, solid, organic substance, but affected only its contained nutrient
juices, that in a stem out of the perpendicular direction those juices
would be drawn to the lower side, which would consequently be more
actively nourished, thence would grow more vigorously in the longitu-
dinal direction than the upper side, and so cause a curvature of the stem
upwards. If this explanation were correct in regard to the roots, it
would follow from it that the point of a root could not penetrate into a
fluid of greater specific gravity than its own substance ; but the experi-
ments of Pinot, Mulder, and Durand (“ Ann. des. Se. nat. 3 Sér,” ii. 210—
Botanical Gazette, i.) shew, that the radicles of germinating seeds pene-
trate into mercury, whence it is clear that the points of the roots are not
directly attracted downwards by gravity, but that the latter causes alter-
ations in the root, through which an active curvature downwards is
brought about. We find indicated here an explanation which bears a
certain resemblance to Knight’s explanation of the growth of the stem.
With reference to the latter, it is at once clear that Knight regarded as
a self-evident fact, the circumstance that the curvature of the stem is a
consequence of its growth. But this seems in the highest degree impro-
bable, if we note on the one hand, that in many organs, even when they
exhibit no further growth (as in leaves, tendrils, &.), curving movements
oceur which depend upon a frequently very transitory expansion of their
cellular tissue wholly independent of their growth ; and remember, on
the other hand, that nothing is more common in stems and branches,
than the manifestation of a much more vigorous growth on one side,
giving to them a very eccentric position, without any curvature being
produced by this one-sided growth. Still less tenable must this explana-
tion appear when we consider that the direction upwards does not occur
in the stem of all plants, but that many follow a horizontal course, and
that the shoots of many plants, for instance, of the Weeping Ash, have a
very strongly marked tendency to grow downwards, without any ob-
servable occurrence of a diffence in the mode of growth from that of the
stems growing upwards. This indicates that there must exist in the dif-
ferent stems differences of organization unconnected with their longitu-
dinal growth, on which it depends that the same external conditions
cause in one a curvature downwards, and in the other a curve upwards.
That these modifications of the internal organization are based upon con-
ditions not very readily detected, may be concluded from the fact, that
the shoots of different varieties of the same plant, as of the Ash or Beech,
may behave quite differently in this respect ; that in almost all our trees,
for instance in the Firs, a difference of direction exists between the
primary and secondary axes, and that frequently, on a sudden, without
perceptible external cause, the points of one or more secondary axes turn

ete EM STA I EET TI LE

ind

THE VEGETABLE CELL. 145

upward and grow in the vertical direction in the manner of the trunk, of
which large specimens of Pinws Cembra in particular exhibit the most
beautiful and striking examples.

To Dutrochet belongs the merit of having called attention to the dif-
ference between the organization of the stem and the root, which must
incontestibly be taken into consideration before all else, in discussing the
movements now referred to, and gives hope that their further investiga-
tion will solve much that is still doubtful in respect to the movements of
plants. Dutrochet (“i émoires,” ii. 1) endeavoured to trace the curva-
ture of the stem upward and that of the root downward from the endos-
mose exercised in the parenchymatous cells of these organs. He found
that a plate cut longitudinally, in the direction of a radius, from an her-
baceous stem, curved in water so as to render the epidermis concave ;
while a plate cut out of a young root exhibited the opposite curvature.
The cause of these different curvatures he found, in the decreasing size of
the pith-cells from within outwards in the stem (these alone coming into
consideration on account of the preponderating size of the pith and the
proportionately small thickness of the bark), and in the decreasing size
from -without inwards of the cortical cells of the root, these alone being
of importance in regard to the root where the rind is so much more deve-
loped. This tendency to curve exists, although in less degree, when the
different parts are not placed in water, in consequence of the cells being
fall of sap, as in the natural condition of plants. The different sides of
the root and stem possess the tendency to this curvature in an equal
degree so long as these organs are in a perpendicular position, and thus
the force of one side is kept in equilibrium by that of the opposite side.
But when a stem or root is placed in an inclined position, according to
Dutrochet’s view, the effect of gravity causing a flow of the concentrated
sap toward the lower side of the organ, limits the endosmose exercised
by the cells of this side, while the cells of the upper side which come in
contact with a less concentrated sap are unrestrained in their endosmose,
and in their expansion consequent thereupon. Thus the tendency to
curvature arising from the endosmose in these acquires the preponderance,
‘and causes an upward curvature of the stem and a downward of the root.
Notwithstanding that many errors occur in the statements of Dutrochet’s
treatise, and that the manifold modifications which present themselves in
the directions of stems and shoots in different plants, a few only of which
have been indicated above, cannot as yet be explained from their struc-
ture, yet this author has the credit of having demonstrated the element-
ary truths: 1, That the curvature of the root and the stem is independ-
ent of their growth ; 2, That the moving organ must be looked for in
the soft parenchymatous cells ; and 3, That the curvature effected by the
cells is not produced by a contraction of that side which becomes con-
cave, thus drawing over the other part of the organ, but, on the contrary,
the curvature arises from a swelling of that side of the organ which be-
comes convex.

aa See
esa para Sica ¥

iit ie matt A HO IS ?
5 an cea RI = mre :

Both stem and root are only capable of retaining the perpen-
dicular direction which they assume through the influence of
gravity, when they are wholly removed from light, or light is
freely admitted to all sides of them ; when the light shines only

Li

146 | ANATOMY AND PHYSIOLOGY OF

on one side of a plant, the latter becomes more or less diverted
out of its normal direction.

It is an every-day’s experience that this is the case in a high
degree with young and still soft stems, since in plants which re-
ceive light on one side only, the stems curve strongly towards the
side whence the light comes. In plants which are very sensitive
to light, like germinating Crucifere, I found that the influence ot
light might wholly overcome the effect of gravity, for when I sus-
pended some of these in a horizontal direction, in a blackened box,
closed on all sides and at the top, and lighted through the open
lower end by a mirror, the plants were compelled to turn their
stems vertically downwards.

This curvature is produced in unequal degrees by the differently
coloured rays of the spectrum, and this independently of their
illuminating power, being caused most of all by the blue rays;
and, according to Payer (“Comptes rendus,” xvii), in general
only by that part of the spectrum lying between F and H, a
statement, which, however, would undergo some modification
through the experiments of Dutrochet (which, it is true, were not
made with the aid of a heliostat, but with red glass, and conse-
quently were imperfect), for according to these experiments, even
the red rays produced curvature, although in slight degree (“Anm.
des. Se. nat. 2 Sér,” xx. 329).

It is proved that this curvature is produced by the illuminated
side, and that the convex side only mechanically follows its cur-
vature, by the fact that when the concave side is removed from
the convex side by a longitudinal incision, it curves more strongly
than before, and the convex side springs back into the upright
position (Dutrochet, “ Mémoires,” ii. 74).

Observ. The fact last stated completely refutes De Candolle’s explana-
tion, which appears, at first sight, to give a very simple cause for the cur-
vature of the stem towards light fallmg on it. De Candolle thought
(« Mém. d. 1. Société d Arcueil,” 1809, ii. 104) that in accordance with the
common experience of plants which receive but little ight growing very
much longitudinally ; plants which received light only on oné side would
grow much longer on the dark side than on the lighted side, and thus
would curve towards the source of light.

We find a similar contrast in the dependence of stem and root
upon light, to that of the movements produced in these parts by
gravity, for the root turns away from the light; a phenomenon
which was first discovered by Dutrochet in germinating plants of
Viscum album, was subsequently demonstrated more extensively
by Payer (“Comptes rendus,” xvi), Durand, and Dutrochet
(“Ann. des. Se. nat. 3 Sér,” v. 65), by experiments, chiefly on the
roots of Cruciferse and Compositee: and of which proof may fre-
quently be obtained in hot-houses, from the aerial roots of Cactus
grandiflorus and other plants. The only cases in which this re-

THE VEGETABLE CELL. 147

treat from light has been shewn with certainty in upward grow-
ing parts of plants, are the tendrils of Vitis and Ampelopsis
quinquefolia, as was first observed by Knight (“ Phil. Trans.”
1812, 314; “ Phystol. Papers,” 164) ; while other tendrils which I
tested in this respect either gave no decided result, or turned to-
wards the light (“Ueb. das Winden der Ranken wv. Schlangpflan-

zen, 77).

Observ. Dutrochet asserts that the stems of all twining plants have
the property of turning away from light. From very numerous obser-
vations on plants with climbing or twining stems, IT must declare this to
be altogether incorrect, for, like other. plants, they turn towards the light.
But I have no definite experience to enable me to decide whether the
hook-like curvature of the end of the stem of Vites, Corylus, ce., and
further, the downward direction of the shoots of Fraxinus pendula, are
(as Dutrochet asserts) to be attributed to the influence of light.

We are quite deficient of anything like a sufficient explanation of the
curvature of plants caused by light. It is not even made out whether
this curvature is a result of an irritability of the cellular tissue, or of the
alteration of endosmotic condition of the cells through the increased eva-
poration caused. by light. The latter hypothesis seems to be opposed by
the circumstance, that these movements occur just as well when the plant
+s under water as when in air ; at any rate we have at present no evidence
that light causes an excretion. of water from the submerged parts of
plants which it shines on, as in plants which are exposed to air. The
curvature does not appear to be any way connected with the presence or
absence of the green colour, since the light-avoiding tendrils of the Vine
are coloured quite as green as the stems of most plants, and since the |
roots of certain plants (of Addiwm Cepa and Allium sativum, according to |
Durand and Dutrochet) turn towards the light. i

An explanation must, of course, give an account as well of why par-
ticular parts avoid light, as of why others curve towards it ; I may, there-
fore, pass over the earlier explanations, which only refer to the latter
point, and many of which are vague in the highest degree, as for ex-
ample “light attracts the plants,” &. ; but the explanation given by
Dutrochet (“ Mém.” ii. 60 ; “ Ann. des. Sc. nat. 3 Sér,’ iv. 72) must be
touched upon. Dutrochet derived the curvature of the stem and root
from the supposition, that the cortical cells of the illuminated side lose a
portion of their sap in consequence of the known effect of light, to m-
crease the evaporation from plants, and the cells therefore contract. It
depends then on the structure of the cortical layer whether, in conse-
quence of such contraction it curves so as to become concave or convex on.
the outer surface ; in the former case, the illuminated organ will curve
towards the source of light ; in the latter case, in the contrary direction.
Now, Dutrochet asserts it is a general rule that the larger cells lie exter-
nally in rind of all those stems which curve towards the light, on which
account when a strip of such rind is laid in water it curves inwards ; a
rind possessing such a structure, in consequence of this, curves outward
and draws the stem with it, when it loses part of its sap through the in-
fluence of light. On the other hand, ail stems and roots avoiding light
possess a rind of opposite structure. In criticising this theory we will

L 2

148 ANATOMY AND PHYSIOLOGY OF

leave out of the question the doubt above referred to, the complete un-
certainty whether light can cause greater amount of discharge of aqueous
Juices from the cells of the illuminated side of the rind of plants lying
under water ; but we must therefore the more distinctly advance that the
statements of the anatomical facts given by Dutrochet are altogether
erroneous, he himself having contradicted these statements by anatomical
facts mentioned in other parts of his writings. With regard to the rind
of the stem of plants striving towards light, the statement that these
curve inwards in water is most decidedly incorrect, of which I have con-
vinced myself in a great number of plants, and in particular in the Phy-
tolacca decandra, especially cited as an example by Dutrochet, for the
rind of all the plants which I investigated in reference to this question
curved outwards in water. It is equally untrue that the rind of roots
curves outwards, for in most roots just the opposite occurs. But when
Dutrochet, in explaining the avoidance of light by roots, ascribed the said
structure to their rind, he forgot that he had stated directly the reverse
of this structure of the rind, in explaining the direction of the root down-
ward. In this way he mixed the anatomical facts together, like a con-
juror does his cards, just as they were requisite at the moment to explain
any movement. Dutrochet had still another subsidiary hypothesis for
the explanation of the movement of the stem, according to which the
fibrous parts of the stem, 7.¢., the young wood, were caused to curve out-
ward by absorption of oxygen. He states that as light sets free oxygen
in the green cells of the rind, a portion of this is conveyed to the young
wood, the latter then, by curving, assists the curvature commenced by
the rind. Disregarding the fact that the entire theory of the curvature
of the wood through the absorption of oxygen rests upon very uncertain
experiments, two circumstances are opposed to it ; in the first place, the
curvature of plants is almost exclusively produced by blue light, while this
is completely incapable of causing evolution of oxygen from green parts ;
in the second place, according to Payer’s experiments (“Comptes rendus,”
1842, 26th December), the curvature takes place also in nitrogen and hy-
drogen. Since the pretended curvature of the young wood would be in the
way of the movement from the light in the tendrils of Vitis, in the shoots
of the Weeping Ash, &c., they are eliminated by the statement that in these
plants the young woody layer is so thin and weak that its effects are im-
perceptible. Itis clear the author knew how to get out of a difficulty.

While the stem and the root only exhibit movement when they
seek to regain the natural position out of which they have been
removed, it is different in the leaves, for these have not only the
power, in a high degree, of returning to their natural position,
when artificially disarranged, but (with the exception of the stout
leathery or fleshy leaves) almost all thin leaves, and particularly
compound leaves, present different arrangements by day and by
night, a phenomenon to which the terms sleeping and waking
have been applied. As in the stem the normal position is the
perpendicular, with the point of the stem turned upwards, so in
the leaf is the horizontal, in which its upper, darker-coloured sur-
face is turned towards the sky ; into this position it is brought |
back by the influence of gravity, when it is disarranged, and it is /

_ THE VEGETABLE CELL. 149

diverted from it by the influence of light falling obliquely on it,
or artificially thrown upon it from below, the leaf constantly
striving to turn its upper face to the light.

The movements which the leaves make under these circum-
stances frequently take place so quickly, that the leaves of many
plants follow the daily course of the sun; at the same time they are
often far more extensive than those movements we observe in the
stem. Not only is the leaf in general far more capable of curva-
ture of its flat and extended substance, in consequence of the
greater pliancy of this than the axial organs, but the movement
of the whole leaf is favoured by the circumstance that in a great
number of leaves, there lie, both at the base of the petiole, and
in compound leaves, also at the base of each leaflet, little enlarge-_
iments (articulations) composed of soft, succulent parenchyma,
which, on account of the abundance of their cellular tissue, and
because, at the same time, the vascular bundles passing down
through the middle of the articulation can oppose but slight re-
sistance to the curvature, are capable of a far stronger degree of
curvature than the other stem-like parts of the plant.

That the various positions to which the terms waking and
sleeping are applied, are produced by the alternating influence
and absence of light, and that the diminishing temperature and
increasing moisture of the air coming on with night, do not play
any essential part in this, is shewn especially by the experiments
of De Candolle, who succeeded in reversing the periods of the sleep-
ing and waking of plants, by illuminating them at night and
keeping them in the dark by day. In very sensitive plants, also,
artificial withdrawal of the light, even for a short time, as the
dim light which exists during a great eclipse of the sun, suffices
to make the leaves go to sleep ; while, on the other hand, many
plants, especially the different species of Owalis, require bright
sunshine to make them expand their leaves fully.

The movements made by leaves in going to sleep differ in the
highest degree in different plants: sometimes they consist of a
sinking, sometimes of an elevation, of the leaf, in compound leaves
at once of sinking, elevation or twisting, sometimes of folding to-
gether of the leaflets ; in general the leaves present a smaller
expansion during sleep than by day, not, however, so that we can
say with E. Meyer, they always seek to return to that position
which they possessed in the bud ; since not unfrequently, for ex-
ample in Ozalis, the position of the sleeping leaf differs essentially
from its position in the bud. ‘Neither must the term sleep lead
to the assumption that the movements by which leaves pass into
their nocturnal position depend upon a relaxation, since, on the
contrary, the parts from which the motion issues, that is the joints,
are in a state of considerable tension during the sleep of leaves.

The flowers of a large quantity of plants exhibit changes of
position by night analogous to those of leaves, the corollas fold-

0 ANATOMY AND PHYSIOLOGY OF

ing up; in the Composite the capitules shutting up, &e. Here
also the times of sleeping and waking have been reversed by
artificial illumination (Meyen, “ Physiologie,” 11, 495).

Undoubted as it is that the movements of sleeping and waking,
both in leaves and in flowers, are dependant upon the influence
of light, yet they do not always occur in such a way that the
waking takes place in the morning when the daylight has reached
a certain definite degree, and the sleep begins in the evening
when the twilight has brought the light down to the same de-
gree, but the waking frequently precedes the dawn of day by
several hours (¢.g., in the leaves of Mimosa pudica), while the
sleep commences when there is still tolerably strong light. This
condition presents itself in a still more striking degree in many
flowers, than in leaves. As a general rule, the openness of the
flowers is indeed regulated by the light, so that the majority open
in the morning from six to seven, and close in the evening at
from six to seven, but in many flowers the opening takes place at
the very commencement of dawn, while they go to sleep even
before noon, or at least early in the afternoon; on the other hand,
some plants require a longer illumination by the sun to cause
their opening, so that the flowers of various plants open gradu-
ally at the different hours of the morning until noon, on which
peculiarities Linnzeus founded his “flower-clock.” These varia-
tions may be partly independent of light, and may be caused by
the circumstance that every species of plant requires a certain
degree of temperature to open its flowers. (See Fritzsche, “ Sitz.
bericht der Acad. zu Wien,” Jan. 10, 1850.) In the flowers of
many plants we meet with the remarkable deviation that they
open first in the evening, reach their full expansion at midnight,
and close again in the morning, a phenomenon which, so far as we
know, has no parallel in the leaves ; perhaps this phenomenon is
analogous to the circumstance that the tendrils of Vitis turn
away from the light.

Observ. Since the far simpler movements which the influence of light
produces in stems and roots have not yet been adequately explained, we
can much less expect that the experiments to elucidate the movements of
leaves should have been more happy. ‘The full development of the cel-
lular tissue in the articulations of the leaves renders it much easier to
demonstrate in them, than in the axial organs of plants, that the motions
of plants are caused by curvature of the parenchymatous tissue, and not
by contraction of the spiral vessels or elongated cells (as was assumed by
Malpighi and all physiologists up to Link’s time, evidently misled by an
erroneous idea of analogy between the movements of plants and those of
animals depending upon contraction of the muscular fibres). To demon-
strate this is merely required the easily performed experiment of cutting
away the cellular tissne, without injuring the vascular bundle, in the
articulation of any leaf possessing a distinct thickening there ; this opera-
tion lames the leaf. Our whole knowledge is essentially confined to this

THE VEGETABLE CELL. 151

fact. For, much as has been written concerning the sleep of plants,
nothing whatever is yet made out of the manner in which light acts upon.
the cellular tissue, whether, as Treviranus assumes eg zs ysiologie.” il. 7 50),
the activity of the latter is excited by light in consequence of an irri-
tability of the cellular tissue ; or, as Dutrochet thought (“ Mémoires,” 1.
525), the excretion of oxygen occurring under the influence of light
brings about an increased ascent of sap, and a consequent turgescence of
the cellular tissue, or, on the contrary, according to Dassen’s hypothesis,
superabundance of crude sap produces the nightly sleep ; or whether, as
Macaire supposed, the absorption of carbon, combined with excretion of
oxygen, occurring under the influence of light, is to be regarded as the
cause of the movement. In particular the variations in the movements
of leaves, some of which sink down while others rise up in sleep, have
not yet been traced back by anatomical research to any definite diffexence
of organization. It is true Dutrochet (“ Mémoires,” 1. 469) took much
sains in endeavouring to make out the cause of motion through anatomi-
cal investigation of stems and leaves, whereby he arrived at results similar
to those in his above-mentioned investigation of the axial organs, since he
thought he found, besides the curvable cellular tissue, a curvature of the
young fibrous tissue produced by absorption of oxygen ; but a minute
exposition of his views appears to me to be superfluous. The complaint
has been made, in other quarters, of the work of Dutrochet, that it is
incomprehensible. 1 would not complain of this so much, as that the
illogical conclusions of the author, and the arbitrary style in which he
introduces unfounded statements of facts (with which T have already
found fault above), have increased in proportion with the complication of
the phenomena which were to be explained. A wide but difficult field
still lies open here to the experimental physiologist.

Besides the movements already described independent of ex-
ternal material influences, peculiar motions of particular organs
are met with in a number of plants, ensuing only through the

action of stimuli accidentally effecting them, whence a sensitive-
ness or irritability has been ascribed, to these plants.

Observ. We meet with such phenomena of irritability in the leaves of
a not very large number of plants of the families of Leguminose, Oxa-
lide and Droseraceex. Among the Leguminose, it is principally in plants
‘of the genus J/unosa, of which I. pudica, above all, has been the sub-
ject of minute investigation ; besides these, there are the various species
of Robinia, and some species of Aischynomene, Smitha and Desmanthus ;
in the family of the Oxalidez probably all the plants possess more or less
distinct traces of irritability, but only the pinnate-leaved Biophytum sen-
sitwwwm in a high degree ; among the Droseracer, the leaves of Dionwa
muscipula have a most remarkable irritability, while our indigenous spe-
cies of Drosera only exhibit traces of it.

In my opinion, a dull irritability exists in the stems of twining plants,

and tendrils.
_ ‘The same property is exhibited also by the stamens of species of Ber-
‘ beris and Mahonia, by Sparmannia africana, of many species of Cactus,
Cistus, of many plants of the section Cynarocephale ; moreover by the

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es

pit Rn A al ee eR TO TE

152 ANATOMY AND PHYSIOLOGY OF

stigmas of Martynia and Mimulus, the style of Goldfussia amisophylla,
and the column of the style of Stylidiwin.

Among the plants possessing irritable organs, Mimosa pudica
especially has been the subject of repeated investigations. The
common petiole of this plant is connected with the stem by a
much enlarged articulation, and similar articulations are met with
at the bases of the secondary petioles and of the individual leaflets.
When strongly irritated, as for example by shaking, the entire
leaf sinks by a bending of the articulation situated at the base of
the inner petiole, the secondary petioles approach together, and
the leaflets, curving forwards and upwards, apply themselves to-
gether, like tiles on a roof, upon the secondary petioles, so that
the whole leaf assumes the position of a sleeping leaf, which gave
rise to the idea formerly entertained generally, that this motion
is the same as that which occurs when the leaf goes to sleep, an
opinion incorrect in many respects. .

The motion of the articulation of the petiole may he produced
by direct irritation of it, but the stimulus must act upon the
under side of the joint, that becoming concave in the motion ;
even a slight touch upon the joint in this part will cause a sink-
ing of the leaf, while strong stimulus, even wounding, of the
upper side of the joint has no effect. But at the same time sti-
mulus affecting other parts of the plant is propagated to the joint
and causes it to move, provided the irritation be strong enough.

The articulation is composed of an accumulation of parenchy-
matous cells containing chlorophyll, each also exhibiting in its
interior a larger or smaller globular mass of a substance strongly
refracting light (oil?). The latter substance, however, does not
appear to be essential since it is absent from the cells of other
irritable organs. Through the middle of the joint run the vas-
cular bundles entering the petiole, united into a comparatively
slender cord. There is nothing at all peculiar in these anatomical
conditions, they perfectly resemble what we find in many other
plants, not irritable. The only circumstance to be regarded as
essential is, that the parenchymatous tissue existing in compara-
tively large quantity, exhibits a considerable distention, so that it
strives to occupy a larger space than is allowed by the mechanical
conditions in which it is placed. If we cut a plate longitudinally
out of the middle of the joint, which of course will consist of the
woody bundle in the middle, and of a layer of parenchymatous
cellular tissue at each side, and then cut this plate lengthways
into thin strips, the middle of which is composed of the vascular
bundle, and the two sides of cellular tissue, the latter pieces
immediately expand about 1-5th longitudinally, whence it is evi-
dent that the vascular bundle is too short in proportion to the
turgescent mass of cellular tissue of the articulation, and that the
latter is compressed in the direction of the longitudinal axis in
the uninjured joint,

THE VEGETABLE CELL. ~ 153

Observ. According to the description. of Dutrochet (“ Rech. sur la
struct. intime des anim. et veget.” 1824 ; “ Nowvell. rech. sur P endosmose,”
1828), and Briicke (“ Miiller’s Archiv.” 1848, 434), the cellular tissue both
of the upper and under side of the articulation has a tendency to curve
inwards strongly. I do not find this confirmed. Of course, if a strip of
the vascular bundle is left connected with the inner side of the plate of
parenchyma above-mentioned, only the outer side of the cellular tissue
can expand, while expansion is prevented on the inside by the rigid
vascular bundle ; under these circumstances a curvature of the whole
plate must naturally take place.

In uninjured articulations, the expansion of the cellular tissue
of the upper side maintains equilibrium with the cellular tissue
forming the under side, which prevents curvature of the whole.
But if the cellular tissue is cut away down to the central vascular
bundle on the upper side of the articulation of a leaf still attached
to the plant, the cellular tissue of the under side having now lost
its antagonist can pursue its expansion, and the leaf thus becomes
at once pressed upwards at a sharp angle ; the reverse occurs
when the cellular tissue of the under side is removed.

Observ. This fundamental experiment which first threw light upon
the anatomical system by which the movements of plants were caused,
was made as early as 1790 by Lindsay, but was again forgotten, so that
the discovery he established was made a second time by Dutrochet (“Sur
la struct. intime,’ de. 1824).

According to the common statement, which rests upon the
experiments of Dutrochet, a leaf robbed in the above described
way of one side of its thickened joint, loses its power of motion
entirely, and after the removal of the lower portion of the cel-
lular tissue of its articulation can rise up no more, and can sink
down no more after the loss of its upper portion. But, as Briicke
(“L. ¢.” 452) correctly observed, this is not altogether true, since
such a leaf still performs the movements of sleeping and waking,
although in a much less marked degree (especially when the cel-
lular tissue of the under side is removed) ; and moreover, as will
be mentioned farther on, has not altogether lost its irritability.

It is clear that the movements of a leaf upwards and down-
wards, dependant upon one-side expansion of the cellular tissue
of the articulation, may take place in a variety of ways. In the
first place, if the cellular tissue of the upper side. swells up and
thus acquires a preponderance over that of the under side, a cur-
vature downwards must take place, and, vice versa, swelling of
the under side of the tissue must raise the leaf; on the other hand,
the same result must occur when the cellular tissue of one side
becomes lax, and thus gives that of the opposite side the oppor-
tunity of following its natural tendency to expand. It is possible
also that both these conditions may exist at the same time.

From the erroneously assumed immobility of a leaf, in which

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Fe a te ined

Sa

154 ANATOMY AND PHYSIOLOGY OF

the cellular tissue has been cut away from one side of the articu-
lation, Dutrochet (“Nowv. rech. sur V endosmose,” 47), drew the
conclusion, that the movement of the leaf always occurred through
the cellular tissue of that side of the articulation which becomes
convex in the curvature, expanding actively, while the tissue of
the side which becomes concave remained perfectly passive. As
already observed, the fact upon which this conclusion rested, is
not perfectly correct. A leaf which has had the upper side of its
articulation cut away, of course immediately rises up nearly per-
pendicular, but it does not remain in this position ; in a few days
it recommences the performance, more weakly though it be, of the
sleep-movements (sinking and rising). It is, therefore, clear that
the expansion of the under side of the articulation, produced by
removal of its antagonist, as a general rule, raises the leaf higher
than in the natural condition, yet at the same time that this ex-
pansion is not constant, but undergoes a daily increase and de-
crease. The same circumstance (only in less degree) presents itself
after the under side of the joint is removed. We must conclude
from this that the expansion of one side of the articulation plays
the principal part in the elevation and depression of the leaf, but
that in this motion the opposite side likewise undergoes a change,
and, indeed, a relaxation.

If the said view of Dutrochet was not wholly correct in regard
to the sleep-movements, still less was it in reference to the irritable
movements. It is clear that if the depression of a leaf resulting
from irritation is caused by the active expansion of the upper
side, overcoming the resistance of the under side, the tension must
inerease in the whole articulation, and the latter must become
rigid. Now, Brucke (“t. ¢.” 440) shewed that the articulation of
an irritated leaf becomes in no slight degree relaxed when this is

- depressed ; we must, therefore, assume that the motion arising
from irritation depends not upon an increased expansion of the
upper side of the joint, but principally upon a relaxation of its
under side. This is also borne out by the circumstance, that a
leaf of which the upper side of the articulation has been cut away,
sinks (although not to the same extent as an uninjured leaf) when
irritated, which would be impossible if the movement had its
source solely on the upper side.

This relaxation, as Brucke also shewed, either does not occur at
all in a sleeping leaf, or at least in a far weaker degree than in an
irritated leaf. Hence it is clear, as I formerly remarked on other
grounds (“Ueb. die Reizbarkeit der Blatter von Robinia.”—Mohl,
“Verm. Schrift.”), that the movement of irritability is not identi-
cal with the sleep movement. Evidence of this is also offered by
the circumstance, that a sleeping Mimosa leaf is at least quite as
sensitive to irritation as a waking one, and performs the move-
ments of irritability very rapidly and to quite as great an extent.

Concerning the internal occurrences, on which the relaxation

THE VEGETABLE CELL. 155

of the lower half of the articulation, resulting from irritation,
depends—whether, as Brucke assumes, but as appears to be highly
improbable, a portion of the cell-sap issues out into the intercel-
lular passages, or a relaxation of the cell-walls takes place—we

know simply nothing.

Observ. Dutrochet subsequently (“ Jf Zmoires,” i., 587) retracted the
theory above-mentioned, concerning the depression of an irritated Mimosa
leaf, and set up the opinion that this movement downwards does not
depend upon the expansion of the cellular tissue of the upper side of the
articulation, but upon curvature of the younger layers of wood, which,
in consequence of the irritation, absorb oxygen from their vicinity in a
way not further explicable, and are thereby caused to curve downwards.
After a short time, and from an equally unknown cause, this oxidation
of the fibrous tissue ceases, the power of curving belonging to the cellu-
lar tissue again acts, and causes the elevation of the leaf. Leaving the
arbitrary character of the whole of this explanation out of the question,
there ig evidence against Dutrochet’s theory in the experiments of Brucke,
which indicate that the depression of the leaf is connected with relaxation
of the articulation, for if the articulation were bent by the curvature of
the woody bundle, the cellular tissue of the under side would be strongly
compressed, which must rather increase than diminish the tension of the
joint.

The leaf of Mimosa is sensitive to stimuli of every kind ;
shaking, wounding, burning, contact of irritating fluids, electric
shocks, &e., all act in the same manner. Quick repetition of an
«rritation exhausts the sensitiveness towards it tolerably soon.
The more vigorous the vegetation of the plant is, the higher the
temperature in which it is placed, the more sensitive it is found
to be.

It has already been observed that the direct irritation of the
articulation of the leaf is not necessarily required to produce the
movement of irritability, but that the effect of a stimulus acting
on a distant part is conducted to the articulation, under which cir-
cumstances, it depends on the irritability of the whole plant and
the strength of the stimulus, how far the manifestation of irrita-
bility becomes diffused from the irritated pomt. In reference to
this conduction of the stimulus, the researches of Dutrochet and
Meyen led to the conclusion that it was conveyed by the vascular
bundles, and not by the parenchymatous cellular tissue ; for on
the one side the conduction of the stimulus was interrupted by
cutting away the vascular bundles, and on the other side wounds
on the rind, when the incision did not penetrate the wood, were
not followed by movements of the leaves. This conduction is
comparatively slow ; according to Dutrochet’s measurements, it
amounted to 8—14 millimeters in a second in the petiole, to only
23 millimeters in the stem.

Investigation of the other irritable plants, the leaves of Dionea,
Oxalis and Robinia, the stamens of Berberis, Cactus, &e., fur-

J
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saint lsat oP airattt EA Natt

Saag en are

156 ANATOMY AND PHYSIOLOGY OF

nished no result which admits of any essential addition to what
has been stated of Mimosa. The moving organ was always found
to consist of abundance of parenchymatous cellular tissue, which,
however, did not differ from ordinary cellular tissue in its visible
properties, and the contents of which, in like manner, presented
nothing characteristic, since they consisted of the usual substances,
starch, chlorophyll, &c., so that the conjecture is, indeed, not over
bold, that irritability may be a property belonging to cellular
tissue generally, which, however, can only display itself outwardly,
when developed in a higher degree, and where especially favour-
able conditions exist in the structure of an organ. The circum-
stance which is so distinctly marked in Mimosa, that the side of
the sensitive organ, which becomes concave in the movement, is
alone capable of receiving the stimulus, while the opposite side is
perfectly insensible, appears to be universal; at all events this
condition exists in like manner in the leaves of Dionwa, the
stamens of Berberis, and in tendrils.

In the majority of cases, the movement of an irritable plant is
very transitory, when the plant is not organically injured by the
stimulus applied. Few experiments have been made on the
effects of long-continued irritation. An experiment of Desfon-
taines affords evidence that a plant may become accustomed to
a weak stimulus; that author carried a Mimosa with him in a
coach, and in a short time the plant became accustomed to the
jolting motion, and its leaves, which at first had closed up, re-
opened. It is otherwise with tendrils and twining plants, which,
when they come in contact with a foreign body, curl over the
point of contact, and in this way partially embrace the support.
A return to the former position is impossible, since through this
| curvature a portion of the tendril or twining stem lying above
| the point first irritated is brought in contact with the support,
_ and in like manner stimulated to the curving movement ; in this
| way the movement of curvature advances up the plant until the
| whole length has become wound round the support.

Observ. The view propounded by me (“ Ueber den Bau und das Winden
der Ranken und Schlingpflanzen”) that the curling round the support
results from an irritability excited by contact, has not had to boast of
any particular approval, yet I do not find that anything better has been
put in its place. When Treviranus (“ Physiol.” ii. 746) says that this
phenomenon is caused by a slowly and inertly acting elasticity, which is
chiefly called into activity by contact with foreign bodies, I must confess
that the meaning of these words is quite incomprehensible to me ; and
when Schleiden (“Grundztige,” 2. ed. xi. 543) states it is a phenomenon of
growth, which determines the direction, that is, the peculiar form of the
tendril, and the growth of the twining plant, he appears simply to be
ignorant of the fact which comes under consideration, since every accu-
rate examination of tendrils and twining. plants shews that the curling
round the support isa phenomenon totally independent of the growth.

THE VEGETABLE CELL. 157

The external action of ponderable or imponderable agents is
necessary to the production of all the movements hitherto men-
tioned ; but besides these, there occur in isolated cases motions
which, so far as existing experience reaches, are wholly independ-
ent of external influences.

It is held as an enigmatical phenomenon. that a twining plant
which stands at a distance of one or more feet from its support,
reaches this in order to grow up it; the cause of it is sought
sometimes in a mysterious power in these plants of seeking out
the supports, sometimes in their asserted property of turning
away from light, &., but the matter is explained in the simplest
manner by a peculiar motion. with which the stems of these plants
are endowed. The younger internodes of twining stems are quite
straight and their vascular bundles run, like those of other stems,
parallel with the axis of the stem ; but, when an internode has
attained a certain age it begins to curl (according to the species
of plant, to the right or left) around its own axis, in consequence
of which the vascular bundles acquire a spiral course. This curl-
ing occurs only in a short length of the stem in each single period
of time, but it advances gradually from below upwards, proceed-
ing from one part of the stem to another, without ever becoming
recurrent The upper part of these stems, always slender and
pliable, hangs over in a curve ; and since it must follow the curl-
ing of the lower part, it is continually carried round in a circle
like the hand of a clock; then if a solid body stands within the,
circle described by the point of the stem, the latter becomes pressed |
upon the solid body, the irritability peculiar to it becomes excited, |

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and thus the twining round the support is produced. (For the \

more minute details of this process, see my essay above referred
to.) We do not at present possess an explanation of these move-
ments and of the circumstance that they occur constantly, either
to the right or to the left, in each species of plant; but it cannot
be doubted that the movement here also has its origin in the
parenchymatous cellular tissue, since the perfectly visible distinc-
tion between the stems of twining plants and those of other vege-
tables, depends on the relative abundance of succulent cellular
tissue in the former, and since in many plants, ¢.g., in Cynanche
Vincetoxicum, the stem becomes more inclined to twine, the
more its succulence is favoured by the shade and moisture of the
locality in which it grows.

Observ. The circular movement of the stem just described has nothing

to do with the twining round the support ; in fact, that part of the stem
which has undergone the torsion is incapable of twining round a support,
and the movement of curvature, which causes the twining, occurs only in
the younger part of the stem, the fibres of which still retain their straight
course. This may be caused not only by the younger parts of the stem
being the softer, more juicy, and, in consequence of this, more moveable,
but also, and principally, by the circumstance that in old curled parts of

158 ANATOMY AND PHYSIOLOGY OF THE VEGETABLE CELL.

the stem the cellular tissue of the rind has already attained a considerable
longitudinal extension, compared with the parts situated nearer the axis.

Whether the movements which Dutrochet observed (“ Ann. d. Se. nat.
2 Sér.” xx. 306) in the stems of Piswm sativwm, are identical with the
above-described circular movements of twining plants, with which, as I
shewed in the “ Botanische Zeitung,” 1845, 118, Dutrochet was but very
imperfectly acquainted ; or whether, as appears to follow from his descrip-
tion, they depend upon a rotation of the stem unconnected with torsion,
I cannot decide, since I have not yet repeated these observations.

Motion is also produced without external influence in tendrils,
which, in like manner, is capable, although in less degree than
the circular motion of twining plants, of bringing them in contact
with foreign bodies. For, when a tendril has attained its fall
(] length, up to which time it is straight, it curls up together spirally
| | from its point to its base, in such a way that its upper side forms
| | the outer side of the spiral. When the tendril is brought in con-
| | tact with a foreign body by this movement, its irritability is

+; excited at the point of contact, and the above-described convolu-
,, tion round the support commences, which progresses from below

|) upwards along the tendril.

' These movements of tendrils and twining plants have not at-
tracted the attention of naturalists in so high a degree as the move-
ments of the leaves of Hedysarum gyrans. This plant possesses
ternate leaves; the middle leaflet exhibits the ordinary sleep-
movements, sinking by night and rising by day, but the very
small side-leaflets present, day and night, a jetking motion, by
which they are alternately raised and depressed. Similar move-
ments are presented by the lateral leaflets of Hedysarwm gyroi des,
according to Mirbel, also of H. vespertilionis, and according to the
statements of Nuttall (“ Genera of N. American ‘Plants,’ ii. 1 10),
those of H. cuspidatwm, and probably of H. levigatum. Few
plants have been so much observed on account of a physio-
logical peculiarity, as Hedysarum gyrans, but unfortunately all
attempts to give a tenable explanation of its movements have
been fruitless.

A similar motion, occurring without external cause, was dis-
covered by Lindley in the labellum of an Orchideous plant, Mega-
cliniwm falcatwm, and more minutely observed by Morren (“Ann.
des Se. nat. 2 Sér. xix. 91). This movement consists of a slow
depression and elevation of the labellum, repeated in periods of a
few minutes. From Morren’s anatomical investigation, it appears
that this motion must be caused by an alternating expansion,
first of the upper, and then of the under, part of the cellular tissue,
which forms the claw of the labellum; but the cause of these ex-
pansions remains just as obscure as that of the movements of the
leaves of Hedysarum gyrans.

WORKS ON BOTANY
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Aas int kia aS ict neat thse nN ote, ee SV Se mA DS tn a Li Pan seminal sr eel 5 - ict ones ial ov CF Gee