funnel-shaped space between the wide micropvle
and the summit of the nucleus. The cellular
tissue of the latter is penetrated by two tubes
emanating from the pollen grains. At the dotted
line the tissue of the ovule becomes continuous
with that of the spermophore.
sac now become larger than the rest, and are
destined to contain the germs of the future
embryos. As their development proceeds,
these bodies, the so-called corpuscula, assume
an elongated, oval form, and the space in-
tervening between their summits and the
membrane of the embryo-sac is occupied by
four small cells on the same level, which ar'e
Fig. 187.
Four cells which surmount the corpusculum of Pinus
sylvestris, seen from above, 200 diam.
* To this tissue is commonly applied the term
albuminous body." It corresponds in its mode of
rierin with the " endosperm " ( 106.") of other
origin with the
Phanerogamia
endosperm" ( 106.)
R 4
REPRODUCTION, VEGETABLE (VEGETABLE OVUM).
248
separated from each other by as many vertical
septa, meeting at right angles. Each corpus-
culum is likewise surrounded on all sides by a
single layer of cellules resembling pavement
epithelium, and exhibits in its interior a nu-
cleus which is usually placed at its superior
extremity. After some time the nucleus dis-
appears, and now a number of transparent
vesicles become visible, which accumulate for
the most part towards the extremities of the
corpusculum,
Fig. 188.
Corpusculum of tlie same in section, immediately be-
fore impregnation, 200 diam.
Its cavity is filled with transparent vesicles, and
bounded superiorly by four granular cells, the
position and relations of which recal very forcibly
the arrangement which presents itself in the
rudimentary archegonium among the higher
Cryptogamia.
104. The growth of the pollen tube, which
has been for many months arrested, at last re-
commences ; the membrane of the summit of
the embryo-sac at the same time becomes
attenuated, and immediately after is pene-
trated by the narrowed end of the pollen
tube, which is brought into immediate con-
tact with the summit of the corpusculum, the
four cells which previously surmounted it
having disappeared. At this time, the corpus-
culum exhibits in its interior, at the end oppo-
site the pollen tube, a single vesicle, much
larger than those by which it is surrounded,
within which is afterwards developed a se-
condary cell, occupying more than half its
cavity. This cell, which is convex above, is
applied by a flattened inferior surface against
the wall of the corpusculum. It soon divides
by a longitudinal septum into two, each of
which is nucleated. These two cells, which
occur throughout the Coniferae, form the
commencement of the suspensor. They next
divide by a second pair of vertical septa, at
right angles to the first; and in each of the
four cells which result, a succession of hori-
zontal septa are formed, by which they are
converted into four vertical columns inti-
mately united to each other. The suspensor
lengthens in one direction only, partly by the
repeated division of the four inferior terminal
cells, partly by the interstitial growth of those
first formed. Soon it bursts through the
Fig. 189.
Corpusculum of the same, 120 diam.
The four cells by which it is bounded superiorly
have disappeared. The pollen tube is still in
contactj by "its flattened extremity with the
corpusculum, and by the rest of its surface with
the cells of the albuminous body, a, 300 diam.
Earlier stage of development of lower end of the
same. A single germ-cell is applied to its wall.
b, 300 diam. Division of germ-cell into four by
two vertical septa, of which one only can be seeu
on section, c and d, 250 diam. Division of the
four resulting cells by a succession of transverse
septa. Above d are two of the numerous com-
plexes of cells, which at this time float in num-
bers in the corpusculum. (From fig. 172 to 189
inclusive, are after Hofmeister).
membrane of the corpusculum at its lower
end, and becomes immersed in the tissue which
occupies the embryo sac, the cells of which,
at the same time, become less intimately
united than before. The four series of cells
of which the suspensor is formed, now separate,
and, from the terminal cell of each, the rudi-
ment of an embryo takes its origin. Its
development commences, like that of the
embryos of theHepaticae and of the first leaves
of the Ferns and Equisetacese, by the repeated
formation of alternately inclined septa in a
terminal cell ; these being followed by vertical
septa radiating from the axis, and, subse-
quently by others parallel to the external
surface. Of the four embryos thus formed,
one only advances to vigorous maturity.
105. Phancrogamia angiospermia. The ob-
servations on record relating to the origin and
development of the embryo among these
plants are now so numerous, that although
the conditions are much more complicated,
and the difficulties in themselves much greater,
we are, notwithstanding, more competent to
draw our conclusions with confidence than
we have found ourselves to be in our previous
study of the Cryptogamia. Among the many
examples at our disposal, we select two of the
simplest, between which, at the same time,
great differences present themselves in those
respects in which the development is variable.
REPRODUCTION, VEGETABLE (VEGETABLE OVUM).
106. Hippuris vulgaris.* The already ana-
tropous ovule of this plant consists of a cylin-
drical nucleus of delicate cellular tissue, along
one side of which is observed a longitudinal
fleshy ridge, terminating above in a short funi-
culus, by which the ovule is suspended from
the apex of the one-celled ovary. One of the
central cells of this nucleus becomes larger
Fig. 190.
249
into a tubular superior, and a spheroidal and
much smaller inferior compartment. The
Section of naked nucleus of Hippuris vulgaris at an
early stage, about 16U diam.
The embryo-sac is seen as a large central nucleated
cell. (Unger.)
than the rest, from which it is further distin-
guished by its containing a free vesicular nu-
cleolated cell-nucleus and granular fluid. This
cell, the embryo sac, rapidly enlarges, and at
the same time assumes an elongated oval form.
A number of vesicles of various size are de-
veloped at the same time, at its micropyle
extremity, all of which disappear some time
before the scattering of the pollen. Shortly
after this has taken place several new cells
are formed, one of which, situated towards
the upper end of the sac, begins at once to
lengthen, and is finally converted into a
tube closed at both extremities (germ-cell).
The rest arrange themselves in vertical series,
so as to form a continuous tissue (the endo-
sperm), which completely occupies the lower
part of the sac. After this, in consequence, as
may be presumed, of the contact of the pollen
tube with the membrane of the sac, the
germ-cell is divided by a transverse septum
* Unger, Botanische Beobachtungen, Entwick.
des Embryos von Hippuris vulgaris. Bot. Zeitung,
1849, p. 329. Sanderson, On the Embryogeny of
Hippuris vulgaris. Trans, of Bot. Soc. of Edinburgh,
Feb. 1850.
Upper end of embryo-sac of the same as observed
immediately before impregnation, 250 diam.
The tubular germ-cell, the lower end of which is
embedded in the nucleated cells of the endosperm,
occupies its axis.
latter, which is the parent cell of the embryo,
is divided by a vertical septum into two
hemispheres. In these two new septa are
formed, also vertical, but at right angles to
The same immediately after impregnation.
The germ-cell is now divided by a transverse sep-
tum into two compartments, the inferior of which
is the parent-cell of the embryo. 250 diam.
the last. In the meantime, several new
vesioles make their appearance in the upper
tubular compartment of the germ-cell, which
eventually become cylindrical, and arrange
themselves, end to end, in its interior. The
four cells of the embryo now divide by hori-
zontal septa, which are succeeded by others
parallel to its surface, and meeting their pre-
decessors at angles of 45. The globular
body which is thus formed, consists of six-
250
teen cells, of which eight are superficial, and
the other eight enclosed as a central spheri-
Fig. 193.
REPRODUCTION, VEGETABLE (VEGETABLE OVUM).
Annals of Natural History : " The ovule
springs from the placental surface as a single
projecting cell, which, by subdivision, soon
becomes a cellular papilla (the nucleus), com-
posed of a central cell (the embryo-sac), sur-
rounded by a simple cellular layer. The two
coats gradually grow up over this, and by the
greater elongation of one side the ovule
becomes anatropous. The nucleus mean-
while loses its cellular coat, apparently by
absorption, and appears as a large oval sac
enclosed in the coats, consisting in fact merely
Fig. 195.
Later stage. Division of parent-cell of embryo by a
vertical septum.
The vesicles contained in the upper tubular por-
tion of the germ-cell have now arranged them-
selves so as to form a filamentous prolongation
to the embryo, about 200 diam.
cal mass. By the frequent repetition of the
same process it increases in size, still retaining
Fig 194.
Isolated sixtcen-ceUed embryo of the same, with its
filamentous prolongation, about 150 diam.
its globular form, until it is transformed into
an embryo, the direction of growth of the
axis of which is downwards.
107, Orchis Morio. In the Orchideae the
structure of the ovule is remarkably simple.
The following description of the mode of origin
and early development of the embryo, in
Orchis Morio, all the stages of which we have
ourselves followed, is taken from Mr. Hen-
frey's paper on Vegetable Reproduction, in the
Early condition of ovule of Orchis mascula.
The embryo-sac is exposed in consequence of the
absorption of the cells which previously sur-
rounded it, 180 diam.
of an embryo sac. In the apex of this,
about the epoch when the pollen falls upon
the stigma, three cellules (embryonal vesicles),
make their appearance at the upper end of
Fig. 196.
Isolated embryo-sac of the same immediately before
impregnation, containing three embryonal vesicles,
180 diam.
the embryo sac, formed apparently by free
cell-formation around a globule of protoplasm.
The pollen masses on the stigma send down
pollen tubes, which traverse the conducting
tissue of the style, and make their way to the
placentas, where they enter, ordinarily, singly
(sometimes more than one) into the micro-
pyle canals of the ovules, and come in contact
with the outside of the apex of the embryo
sac, immediately above where the embryonal
vesicles lie ; but the pollen tube does not pene-
trate the embryo sac. Soon after the pollen
tube has reached the embryo sac, one (very
rarely two) of the embryonal vesicles begins to
swell, becomes divided by a cross septum into
two cells, and while the upper one grows out
in a filamentous form through the micropyle,
by a continued process of cell-division, the
lower cell enlarges, and divides repeatedly so as
to form a cellular globule the embryo, which
in this plant does not go on to produce a co-
tyledon and radicle, as in most other cases.
The filamentous prolongation, the use of
REPRODUCTION, VEGETABLE (VEGETABLE OVUM).
251
which is not evident, but which seems ana- By continuous cell multiplication an organ
logous to the suspensor, presently to be is formed, in which may be distinguished a
mentioned, meanwhile decays away."*
Fig. 199.
Fig. 197.
Ovule of the same at the period of impregnation,
x, the external integument ; c, the internal, which
immediately surrounds e, the embryo-sac. The
pollen tube p, after passing the wide exostome
becomes sensibly narrowed as it penetrates the
canal leading to the embryo-sac, with the out-
side of which its termination is in contact. 180
diam.
108. The anther and the pollen cell. The
history of the development of the anther is
remarkably uniform among the different families
Fig. 198.
The same, some time afler impregnation.
The remains of the pollen tube are observed to be
still adherent to the sac. The rudiment of the
embryo exhibits itself as a somewhat pear-shaped
cell, divided towards its upper part by a succes-
sion of transverse septa, into numerous compart-
ments. The lowest of these, larger and more
granular than the rest, is the parent-cell of the
embryo. 180 diam. (The above, from 191 to 198
inclusive, are original.)
of Phanerogamia. It at first appears in the
young flower-bud as a cellular papilla, which
grows out laterally from the floral axis.
* Henfrey, On the Reproduction of the higher
Cryptogamfa, and the Phanerogamia. Annals of
Nat. Hist., June, 1852.
Further developed embryo. (Orchis Morio.")
The embryo-sac is no longer distinguishable. The
spheroidal embryo which completely occupies
the cavity of the ovule is surmounted by a fila-
mentous prolongation, which projects through the
micropyle. 150 diam. (Henfrey.)
central cylindrical column (connective), along
the antero-lateral aspects of which are at-
tached two larger cellular masses; the outer
surface of each is marked by a vertical furrow,
indicating its division into two halves, which
are the rudiments of the future facuti. In
each half a single axile vertical column of
cells soon becomes distinguished from those
surrounding them by their greater size and
granular contents. In each of these cells
the nucleus disappears, and is replaced by
two others, this being followed by a division
of the cell contents (primordial membrane),
which results in the formation of a new
cell round each nucleus. By the repeti-
tion of this process a mass of cells the
parent-cells of the spores is formed, which
occupies the centre of each rudimentary
loculus. The next change observed is the
thickening of the walls of the parent-cells by
gelatinous deposition on the interior surfaces.
This is followed in all of them by disappear-
ance of the nucleus, and consequent division
of the contents of the cell (primordial mem-
brane) into two portions, each surrounding a
new nucleus. These, however, are only trans-
itory formations, and are soon succeeded by
four permanent nuclei, which are placed
towards the four angles of a regular tetrahe-
dron, each invested with a primordial sac con-
taining a granular mucus, on the surface of
which is soon secreted a gelatinous layer. In
this manner the parent cell is divided into four
compartments the so-called special parent
cells of the pollen grains. Within each com-
partment is now formed a new cellulose mem-
brane on the surface of the primordial utricle.
This is transformed into a resistant and co-
loured tegument, which is the outer mem-
brane of the pollen grain, and exhibits various
projections of its surface, which differ ac-
cording to the species.
109. While these changes are taking place
in the central mass of each loculus, the tissue
forming its wall is transformed into a capsule
of three distinct cellular lavers. Tiie inner
REPRODUCTION, VEGETABLE (VEGETABLE OVUM).
252
layer consists of radiating prismatic cells, and
is soon absorbed. The cells of the second
layer are distinguished by their containing at
first numerous starch granules, and afterwards
by the deposition of spiral fibres on the inner
surfaces of their walls. These are usually
dice-shaped cells arranged in concentric
layers. The external or epidermic layer
consists of tabular cells in contact by their
edges.*
110. Review of the analogies which present
themselves in the history of the development of the
reproductive organs of the higher Cryptogamia and
of the Phanerogamia. The families in question
are distinguished by the presence of what is
called "sexual reproduction" from all others.
It is true that among the Characeae, Conju-
gates, Vaucheriaceae, and Desmidese, the con-
currence of two dissimilar parts is necessary
for the development of the germ ; but in them
the phenomena do not present themselves in
such strict conformity to law, and the anato-
mical relations of the germ to the organ which
contains it are not nearly so complicated as
in the plants under our consideration. Taking
the sexual germ as our starting point, in com-
paring the history of the development of the
phanerogamous with that of the cryptogamous
plant, the following analogies present them-
selves :
1 1 1. 1. Analogies existing between the ovule,
the anther, and the sporangium In Zostera
marina the termination of a stem destined
to bear reproductive organs, is broadened out
in the form of a spatula, concave on one side,
convex on the other. On the concave sur-
face are observed, early in the development,
two vertical series of papillae one on each
side of the middle line which are the rudi-
ments of the organs which support the ovules
and anthers. In each series, the two kinds of
rudiments are arranged alternately in such a
manner, that an ovule in one series is always
on the same level with an anther in the other.
The rudimentary organ which is destined to
contain the ovule, commences as an imperfect
ring of cellular tissue, on the inside of which
is seen a little round projection a bud in
the axil of a leaf. From this projection is
developed the ovule, with its teguments, just
as described in Orchis Morio. The axis of
its nucleus is occupied by a vertical series of
cells. Of these the uppermost enlarges, and
becomes detached from its neighbours, so as
to form the embryo-sac.-)- If we compare this
process with what occurs in Selaginella, we
find in each case, a cell belonging to the stem
in the axil of a modified leaf, which transforms
itself into an axial organ. In each case one
of the central cells enlarges and becomes
detached in Selaginella, to form the mother
* NSgeli, Zur Entwick. des Pollens, &c. Zurich,
1842 ; Wimmel, Zur Entwick. des Pollens, &c. Bot.
Zeit. 1850, S. 225.
f Hofmeister, Entwick. der Zostera. Bot, Zeit.
1851; Grb'nland, Beitrag. zur Kennt. der Zostera
marina, &c. Bot. Zeitung, St. 10. 1851.
cell of four spores in the phanerogamous
plant, to become the embryo-sac.
1 12. The exact correspondence, step for
step, which exists between the development of
the anther, and that of the sporangium, will be
best seen by successively comparing the de-
scriptions contained in 89 and 108. It is
rendered still more striking when we consider
the very remarkable variations which present
themselves in the structure of the anther
among the Phanerogamia themselves ; as e. g.
in Zostera, among the Orchidaceae, and other
examples for the description of which space is
wanting. The contemplation of these analo-
gies leads us to remark how little relation there
seems to be as respects the organs under con-
sideration between the morphological import
of the rudiment and its development. The
ovule of Zostera is an axial organ, originating
in the axil of a modified leaf; its analogue in
development, the anther, is itself a bilateral
foliar organ. The sporangium of Equisetuin
seems to originate as a leaf, that of Selagi-
nella, as an axis in the axil of a leaf.
1 13. 2. Analogy between the embryo-sac y the
pollen cell, and the parent cell of four spores
In approaching this, the most difficult part of
our inquiry, we must refer to the Coniferae, as
holding in so many respects an intermediate
position. Of those stages of the development
which precede the act of impregnation in Se-
laginella, the first, namely, the division of the
parent cell into four compartments, and the
formation of a spore in each, is entirely wanting
in the Coniferae. The prothallium under-
standing by the term the organ of which the
archegonia form a part is represented by the
corpuscula, between which and the archegonia,
the resemblance in structure is very striking.
The difference in the mode of origin of the
germ-cell, on the other hand, is no less re-
markable. "Among the Cryptogamia there is,"
says Hofmeister, "only one germ-cell which
completely fills the central cell of the arche-
gonium, while in the Coniferae, very numerous
germ-cells swim in the central cell of the cor-
pusculum, of which one only, applied against
its lower end, is fecundated." In the gymno-
spermous Phanerogamia, all the steps of de-
velopment which intervene between the parent
cell and the germ, disappear; the latter origi-
nating altogether independently at the upper
end of the embryo-sac. As the transforma-
tion of the germ-cell is the most important
element in the process of development, it
presents the greatest degree of constancy. It
always commences by the formation of one
or more septa, the direction of which, in rela-
tion to that of the first axis of growth, is
transverse or nearly so.
114. In the Hepaticae and Mosses one sep-
tum is formed, the inferior of the two result-
ing cells undergoing no further development,
while the superior is transformed into the pri-
mary axis of the fruit. This fruit-axis, the apex
of which is converted into a sporangium, is
normally a leafless one. In the Mosses, how-
REPRODUCTION, VEGETABLE (VEGETABLE OVLM).
ever, examples frequently occur, in which its
development is changed, under the influence
of peculiar external circumstances, in such a
manner that, instead of producing a sporan-
gium it lengthens considerably, and bears
symmetrically arranged leaves. Such a con-
dition makes" it more easy to compare the fruit
of the Mosses and the leafy stems of the
higher plants. In the Ferns and Equisetaceae,
again, only one transverse septum is formed;
but here, it is the inferior secondary cell
which is developed to the embryo, the
direction of the first axis of growth being
opposite to that of the archegonium. In
Selaginella, a succession of transverse septa
are formed, whence results a conferva-like fila-
ment, which lengthens downwards by repeated
division of a terminal cell. At length the
youngest cell is transformed into an embryo.
Among the Coniferae, the same process pre-
sents itself, with this important difference, that
before it commences, the germ divides by two
crucial vertical septa into four cells, which
correspond to the four embryos which are
afterwards formed. In all the Phanerogamia,
probably without exception, the germ-cell
divides," in the first instance, by a trans-
verse septum into two cells, of which the
upper is the larger. In some cases the lower
cell is developed directly to a spherical cel-
lular mass (as in Hippuris and Orchis Morio).
Much more frequently, however, it is trans-
formed into a conferva-like filament (sus-
pensor) which lengthens by repeated division
of an inferior terminal cell. At length the
youngest cell, instead of lengthening, becomes
spherical, and gives rise to the embryo by a
process similar to that described above in
Hippuris.
1 15. The organ to which the name suspen-
sor is applied by Mr. Henfrey in Orchis Morio,
differs materially from that of Selaginella, the
Coniferse, or from that described in the pre-
ceding paragraph. Its formation does not, like
that of the true suspensor, precede, but follows
the origin of the embryo. In Hippuris, it
appears to result from endogenous cell-forma-
tion in the lengthened upper compartment of
the original germ-cell.
116. The difference bet ween the development
of the pollen grain, and that of the microspore
of Selaginella and of the Rhizocarpeae, is no
less remarkable. Among the Phanerogamia,
after the pollen grain has remained for some
time in contact with the stigma, its inner mem-
brane grows out at one point of its periphery
into a filiform cell ; this lengthens more or less
rapidly until it reaches the micropyle of the
ovule, which it enters, and at last comes into
contact with the embryo sac. The sac
usually resists it strongly ; sometimes it is
bulged in, but is very rarely perforated. In
consequence of this act the transformation of
the germ-cell commences. The absence of
moving filaments among the higher plants
stands connected with the intervention of a
second membrane (that of the embryo sac)
between the two fluids, the union of which
! 253
seems to constitute the essential condition of
fecundation.
117. In comparing the development of the
microspore with that of the spore of the Ferns
with which the plants among which it presents
itself are so closely allied, the difference is
even more striking. In Selaginella all the
steps intervening in the Fern between the
spore and the tessellar cells of the antheri-