into numerous secondary masses, the number
of which is always a power of two. From the
latter is formed a transparent gelatine-like in-
vestment which lines the parent cell. After the
completion of these changes the original cell-
wall is ruptured, and the whole contents
escape in a mass. No sooner has this taken
place than the corpuscles into which the green
protoplasma has divided, commence an active
motion in the interior of the gelatinous cell
in which they are included, and in fact display
in every respect the form and peculiarities of
zoospores. They are not, however, as in
every other example with which we are ac-
quainted, destined to display their activity
beyond the narrow limits within which they
originate. In a short time their motions be-
come languid, and finally cease, while they
arrange themselves in a beautifully regular
geometrical order which corresponds exactly
to that of the cells that constitute the adult
Pediastrum. The next change observed is
the disappearance of the gelatinous membrane,
and the investment of each of the zoospores
with a distinct covering of its own. From this
there results a disc-like body, which, in a
short time, assumes all the characteristics of
the original parent.*
3. Taking these simplest of unicellular
plants as our point of departure, we pass to the
consideration of the confervoid Algae, many
of which, though they are but little elevated
above the Protococci as regards their struc-
tural elements, present a general appearance
which at first sight recalls that of plants very
much higher in the scale of organisation.
Thus in Bryopsis and its allies, in which the
tubular frond branches in the most compli-
cated manner, the whole consists essentially
but of a single cell, the cavity of which is
continuous throughout. When the formation
of zoospores is about to take place, all that
is observed in a Bryopsis is the accumulation
of the green granular protoplasma towards the
* The development of Pediastrum has been de-
scribed by Braun (Die Verjungung in der Natur) as
well as by Caspary (Botanische Zeitung, 1850,
S. 786.). The description in the text is after Braun,
with whom Caspary agrees in every important par-
ticular.
213
extremities of the tubular branches. In these
situations the cavity of the tube becomes
completely filled, while at some point in the
neighbourhood of each accumulation, the tube
membrane becomes sacculated so as to present
a nipple-shaped projection. In the meantime
the accumulated protoplasma is observed to
have given rise, by its division, to numerous
green bodies, the forms of which cannot yet
be distinguished, owing to the closeness with
which they are packed together. No sooner,
however, is this process complete, than a re-
markable phenomenon, corresponding to that
already described in Protococcus, manifests
itself. The crowded zoospores, now com-
pletely developed, at once commence their
characteristic motions. From this results an
appearance of confused agitation, to which
the term " swarming " has been applied by the
Germans. A minute aperture, or pore, is
Fig. 129.
a, termination of tubular frond of Bryopsis crowded
with zoospores ; b, the same, after the escape of
its contents. Each of these exhibits the lateral
pore ; c, fully formed zoospores in active motion,
a and 6 150 diam, c 200 diain.
then found at the extremity of the nipple-like
projection, apparently in consequence of the
absorption of the cell-membrane at its apex.
The zoospores now begin to escape, at first
one by one, afterwards more rapidly, until at
last a few only are left occupying the cavity of
the tube.*
4. In the simplest forms of jointed con fer-
vokls, the frond consists of a series of cells super-
posed one upon the other, each of which is
capable of producing zoospores independently
of the rest. In the vegetative state, each
contains only a green protoplasma. The re-
productive process is the same in every
respect as in the Bryopsideae, the opening by
which the zoospores make their exit, being
situated at the upper part of the cell, imme-
diately below the septum, which divides it from
its successor. In other cases (as in Mi-
crospora), the zoospores escape by a kind of
* Thuret, Recherches sur les Zoospores des Al-
gues. Ann. des Sc. Nat. xiv. 217.
p 3
REPRODUCTION, VEGETABLE (VEGETABLE OVUM).
dislocation of the tube, each cell dividing into
two in a plane parallel to the septa.*
5. The Ulvaceae, among which the frond has
no longer the form of a filament, but assumes
that of a membranous expansion of juxtaposed
cells, still present the same phenomena to our
notice. In the cells set apart for the forma-
tion of zoospores, the green protoplasma is
increased in quantity, at the same time that it
becomes accumulated towards one point of
the cell-wall. As the zoospores are formed,
they are observed to converge with their
apices towards this point. The phenomena
attending their escape from the parent cell are
similar to those which we have already
noticed.
6. In some genera, which seem to be closely
related in form and structure to the Bryop-
sideae, we observe this important difference,
that the zoospores are developed in an organ
specially destined to this purpose, which
presents peculiarities of form distinguishing
it from every other part of the branching
tubular frond. Thus in the genus Derbesia
distinct spore cases are to be observed, the
cavity of which does not communicate with
that of the frond. These organs, which are
of an oval form, take their origin in the same
manner as the ordinary vegetative branches
of which they are modifications. A young
branch which is destined to become a spore
case, instead of elongating indefinitely, begins,
after having arrived at a certain length, to
swell out into an ovoid vesicle, in the cavity
of which a rapid accumulation of protoplasma
takes place. The next change which oc-
curs is the separation of this protoplasma
from that of the rest of the plant with which
it was before continuous, so as to give rise to
an oval and opaque mass, which soon becomes
surrounded by a distinct membrane. As the
result of the division of this mass, a number
of pyriform zoospores, each of which is fur-
nished with a crown of cilia, are set free.
Many other genera have been described by
Derbes and Solier-|-, in which the relations of
the spore cases to the frond are similar to
those which exist in Derbesia, although the
forms presented by the organs in question are
infinitely various.
7. The researches of the authors above
alluded to, along with those of M. Thuret, have
shown us that in many families of the olive-
coloured Algae, the occurrence of zoosporous
reproduction is no less general. The zo-
ospores, however, although they resemble in
their general form those of the plants which
we have been considering, differ from them
not only in respect of their olive colour, but
* In the genus (Edogonium, the protoplasma of
each joint, instead of being converted into a number
of zoospores, goes to form but one, which differs
from those of other genera, in the first place in
being considerably larger, and secondly, in present-
ing around its rostrum not two, but a number of
cilia, which are arranged in the form of a crown.
(See Thuret, /. c. p. 226.)
t Derbes and Solier, Sur les Organes reproducteurs
des Algues. Ann. des Sc. Nat. xiv. 260.
in the arrangement of their cilia. These
organs, which are always two in number, are
Sporangium of Ectocarpus siliquosus, 240 diam.
Ectocarpus is one of the simplest forms of olive-
coloured Algae, consisting of branching, conferva-
like filaments. The extremity of any of the
branches is capable of being converted into a
sporangium by the absorption of the septa of the
terminal cells. The zoospores are arranged in
regular horizontal layers, the positions of which
are indicated in the empty sporangium by faint
markings of its membrane.
usually of unequal length, and emanate not
from the beak, but from the reddish-coloured
point in its neighbourhood. The longest is
directed forwards, being closely applied to the
colourless beak ; while the other, which seems
during the motions of the spore to serve as a
rudder, assumes an opposite direction. In
many genera a peculiarity exists, the significa-
tion of which is not yet completely under-
stood that, namely, of a double fructification.
The ovoidal sporangia (oosporangia y Thur.),
which have been frequently described as single
spores, in reality contain numerous zoospores.
The other form (tricko-sporangium, Thur.) con-
sists of a series of small cells joined together
so as to form a narrow and generally short fila-
ment. Each of the cells contains a zoospore,
which, according to the observations of Thuret,
is no less capable of germinating than the
one produced by the oosporangium. In the
genus Cutleria there is observed, for the first
time, another feature of great interest and
importance ; namely, the appearance of two
kinds of organs which seem to be opposed to
each other as regards their reproductive func-
tions. The sporangia (trichosporangia) of
Cutleria, not only differ from those of other
genera, in respect of their greater size, but
REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 215
present well-marked distinctive peculiarities the resulting cavities, zoospores are to be
of structure. The frond consists of olive- found, which, though they altogether resemble
coloured, irregularly divided Jlabelli, on each in structure those of the other olive-coloured
Algae, are about three times as large. The
Fig. 131. supposed antheridia of Cutleria communicate
^..J*ST to the tufts of which they form a part, their
x ^ characteristic orange colour. The organs
themselves are elongated, sausage-shaped
^^ vesicles: they contain a greyish, granular
matter, in which, as the organ becomes ripe,
indications may be observed of a division into
several concentric layers ; the more internal
of these layers being distinguished from those
next the surface by the greater intensity of
the orange colour which they present. After
Fig. 133.
a, a poi^ion of one of the tufts, or sori, of Cutleria,
showing the mode of attachment of the filaments
which support the sporangia to the surface of
the frond; s, a ripe sporangium. Two others,
half ripe, are also seen. Each is divided into
eight compartments, in each of which is formed
a zoospore, 200 diam. ; b, zoospores ; c, the same
in various stages of germination ; the earliest
stage to the right, 300 diam.
side of which, tufts (son), consisting of the
reproductive organs, intermixed with hair-
like bodies, are scattered at irregular intervals.
The sporangia, and so-called antheridia, are
borne by different individuals, but their po-
sitions and arrangements on the frond are
identical. The former consist of oblong or
club-shaped bodies, which are supported by
hyaline pedicles, set into their inferior extre-
mities. The cavity of each sporangium is
divided by three transverse partitions into
four cavities, each of which is again bisected
by a longitudinal median septum. In each of
Fig. 132.
Contents of anthtridium of the same, 400 diam.
Each antherozoid is an oval hyaline corpuscle,
which moves in the direction of its long axis. It
exhibits towards its posterior extremity a
coloured granule, from which springs a pair of
cilia of unequal length. The longer of the two,
which oscillates rapidly, is directed forwards ; the
shorter, which is motionless, backwards.
the discharge of the contents of the antheri-
dium, it may be observed to consist of a
transparent vesicle, which, like the analogous
female organ, is divided by transverse and
longitudinal septa into eight communicating
cavities.
8. With the organs last described we think
we need have little hesitation in comparing
the structures to which the same name has
been applied, as they occur in the Fucaceae.
The fructification of these plants is, as is well
Fig. 134.
Portion of one of the sori of the male plant of the
same.
The ripe sausage- shaped vesicles, which contain
antherozoids, are shaded. Others are shown
which have already discharged their contents,
180 diam. The transverse markings, much too
distinct in the engraving, indicate a tendency to
the formation of compartments similar to those
which present themselves in the sporangia.
a, antheridia from the conceptacle of Halidiys sili-
quosa, with the filaments on which they are sup-
ported, 200 diam. ; b, antherozoids, 400 diam.
known, enclosed in spherical cavities, situate
under the epidermis of the frond, which are
called conceptacles, and may be male, female,
p 4
REPRODUCTION, VEGETABLE (VEGETABLE OVUM).
216
or hermaphrodite, according to the organs
which they contain. The male concepta-
cles present in their interior an arrangement
of branched filaments, or hair-like organs,
which, taking their origin from the surrounding
cellular tissue, converge towards the pore.
At the summits of these filaments, the so-
called antheridia are supported, which consist
of little ovoid transparent vesicles. They
contain, in their early condition, a granular
protoplasmic material, but as they approach
maturity, the so-called antherozoids make
their appearance. These last are hyaline
corpuscles, not exceeding about &0 * 00 of an
inch in their longest dimension. Each con-
tains a granule of a greyish or reddish orange
colour, from which the organs of locomotion
emanate. The form of the zoids differs ac-
cording to the genus. InFucus, they are bottle-
shaped, and each possesses a pair of cilia, one
of which, the shortest, is directed forwards
from the neck, while the longest emanates
from the coloured point and is pointed back-
wards. In Halidrys, the zoid is ovoid or
spherical, and the longest cilium is directed
forwards. In Fucus and several other genera,
the transparent vesicle in which the zoids are
immediately contained, is itself enclosed in a
second of similar form. At the period of
maturity this last gives way at its apex : the
internal sack is expelled, and at once finds
its way towards the external opening. In
the meantime its delicate membrane disap-
pears, and the liberated zoids commence their
active motions.
9. Although the antherozoids of the Fu-
coideae differ from the zoospores of the other
olive-coloured Alga?, in their not possessing the
power of germination, there are yet remarkable
points of correspondence between them, in
their form, structure, and mode of develop-
ment. Both are composed of a hyaline pro-
toplasma, and the position of the coloured
granule, as well as the arrangement of the cilia,
corresponds. They differ, in the first place, in
size, and secondly, in respect of the chloro-
phylle granules, which are present in the zo-
ospore, but absent in the antherozoid. As
regards the question of their functional sig-
nification, they may be considered, on the
one hand, as the elements of a male secretion,
and the organs in which they are contained,
as antheridia ; on the other, we may look
upon them as the formal representatives
of structures destined in other families to
the performance of functions of which they
are themselves incapable. In favour of the
first of these views we have no direct evi-
dence, and must trust entirely to analogy.
We know that in Cutleria and its allies,
the zoospores display the power of germi-
nating without the slightest reference to the
presence or absence of the secretion of the
supposed male organ. Further, if, as all obser-
vations which have been hitherto made, tend
to prove, the zoospores of all the green Algae,
and of so many of the olive-coloured, normally
germinate under the condition of the constant
non-existence of such organs, it is difficult
to see why an exception should be made in
favour of those of other families in which
they are present. As regards the Fucoideae,
we have certainly no evidence whatever that
the antheridia perform any function, either
more or less important in the reproductive
process.
10. In the family of Vaucheriaceae, the zoo-
sporous reproduction is remarkably modified by
the substitution of a single multiple zoospore,
of large size, for a number of smaller ones.
The frond of Vaucheria consists of a branched
tube, and much resembles in general form,
that of the Bryopsideae, from which the Vau-
cheriae in their vegetative condition differ only
in respect of the arrangement of the chloro-
phylle. The commencement of the formation
of zoospores is announced by the condensa-
tion of the green protoplasma in the rounded
terminations of the branches of the plant.
This condensation is accompanied with an
enlargement of the cylindrical filament, which
soon appears club-shaped, and is completely
occupied by a confused and opaque dark-green
mass. Shortly afterwards a septum is formed,
which limits the terminal portion of the tube.
Within the separate cavity thus formed, the
mass of protoplasma becomes further con-
densed ; its margin being surrounded by a clear
space which intervenes between its external sur-
face and the tube membrane. This body, which
possesses an oval form, is the future zoospore.
No sooner is it completely developed than the
membrane which encloses it gives way at the
apex, and it begins to insinuate itself through
the resulting narrow opening. Having com-
pletely freed itself, it forthwith commences an
active progressive motion, which is accom-
panied by a circumvolution round its axis.
The zoospore at this period possesses no dis-
tinct or consistent investing membrane, as is
evident from the fact, that if, during its escape,
it divides accidentally into two a circum-
stance which not unfrequently happens, from
the relative narrowness of the opening through
which it has to pass each part is complete
in itself and capable of germination. Its whole
surface is covered with vibratile cilia, which
are apparently connected with an epithelium-
like structure. In this arrangement there
seems to be an indication of a tendency to a
division into smaller particles, by the melting
together of a number of which the whole
may be conceived to be formed. Like all zo-
ospores its period of active motion is short; it
soon becomes stationary and begins to germi-
nate.* The zoospores of Vaucheria seem to
correspond closely with the motionless spores
of the true Dictyotaceae (Dictyota, Padina,
&c.), as well as with those of the Fucaceae.
In the case of the latter, the accuracy with
which their structure and germination have
been studied, has enabled us to follow out the
analogy more closely. In speaking of the an-
* See Thuret, Ann. des Sc. Nat. 2 e S. xix. 269 ;
Vaucher, Hist, des Conferves d'Eau douce, p. 246 ;
Karsten, Die Fortpflanzung der Conferva fontinalis,
Bot. Zeit. 5 Stuck, 1852.
REPRODUCTION, VEGETABLE (VEGETABLE OVUM).
theridia ($ 8.), we described the general
form of the conceptacles. In the monoecious
and dioecious Fuci, the female conceptacles
are distinguished from the male by their olive
colour. The spores are developed each in
the interior of a perispore, which is borne on
a pedicle emanating from the inner wall of the
conceptacle. They make their escape by the
rupture of the perispore at its apex. At the
moment at which this takes place, the spore
is perfectly simple, except that in one or two
species the surface is covered with cilia, which
seem to resemble those of Vaucheria. Soon
afterwards, a remarkable series of changes
occurs, consisting in the splitting of the en-
dochrome into a number of masses usually
eight each of which becomes isolated, and
finally assumes the form of a smooth and
spheroidal sporule, provided with an investing
membrane. About twenty-four hours after the
completion of this process, germination com-
mences. It consists in the budding out of the
membrane of each sporule, at some point of
its surface, into a nipple-shaped projection,
which in the following forty-eight hours, elon-
gates into a cylindrical tube; shortly afterwards
the whole body of the sporule is converted by
repeated division into a mass of cells, in which
condition it has been by many writers mis-
taken for the original spore, and described as
such. The Vaucheria? present the peculiarity
of a double mode of reproduction. In the
earlier periods of the growth of the plant,
there occurs the successive formation of aggre-
gate zoospores of large size at the termination
of the branches, as above described. In the
older fronds these are no longer observed, their
place being taken by organs producing germs
which are capable of retaining for a long period
their power of development.
11. In that most remarkable plant the Sa-
prolegnia ferox, which is structurally so closely
related to Vaucheria, though separated from
it by the absence of green colouring matter,
we find a corresponding analogy in the history
of the development. Its vegetative life is, in
fact, divisible into two well-marked periods,
each characterised by a special mode of germ-
formation. During the first, the only one
with which we have at present to do, swarms
of zoospores which rapidly succeed each other,
are formed at the closed terminations of the
cylindrical filaments. The mode of their
origin, agrees with that of the aggregate zoo-
spore of Vaucheria. The protoplasma accumu-
lates in the swollen extremity of the filament,
and a septum is formed in exactly the same
manner as in that plant ; while the mass of
protoplasma is now observed to be limited by
a distinct surface. At this point the resem-
blance ceases ; the protoplasmic membrane
divides, just as in the spore-cases of the zo-
osporous Algae, into particles, which, as the
period of maturity is approached, become more
and more easily distinguishable from each
other. These particles are the future zo-
ospores. Soon they detach themselves from
their connection with the membrane which
encloses them, and with each other, and pre-
217
sent the globular or ovoidal form characteristic
of their perfect condition. In the meantime
the external tube membrane buds out at its
apex, so as to form a conical projection; as
the zoospores become ripe, a gentle oscillatory
motion is seen in the upper part of the spore-
case. This is accompanied with a compres-
sion of its contents, in consequence of which
its membrane gives way at its weakest point,
viz. the apex of the terminal conical projec-
Fig. 135.
Sporangium of Saprolegnia ferox, during the expul-
sion of the zoospores, 200 diam.
(All the figures, from 129 to 135 inclusive, are from
Thuret)
tion. In its most perfect condition, the zo-
ospore of Saprolegnia consists of a pyriform,
protoplasmic, membraneless corpuscle, which
is furnished with a pair of cilia, emanating from
its apex. It is remarkable for the short dura-
tion of its motion, the cessation of which la
immediately followed by germination.*
* For the history of the second period of the
vegetative life of Saprolegnia, see below, 19.
It is only under the most favourable conditions
that the zoospores of Saprolegnia assume the form
described in the text. Very frequently at the period
of their escape, they are sp'heroidal corpuscles unen-
dowed with the power of motion, if uot incapable of
germination. In this case, according to Anton de
Bary, the completion of their development takes
place outside of the spore-case. He describes the
accumulation of the escaped, but imperfectly formed,
zoospores in rounded heaps (Kopfchen), which re-
main for several hours in contact with the termina-
tions of the tubes from which they have escaped,
and finally become invested with a* cellulose-mem-
brane. Within this membrane their development
is completed ; and when they at last escape, they
REPRODUCTION, VEGETABLE (VEGETABLE OVUM).
218
12. In the process of the formation of zo-
ospores in Saprolegnia, we have an inter mediate
step between that of the zoosporous Algae on
the one hand, and that of a class of plants which
is usually placed among the Fungi on the other.
I allude to the Fungi included in the class
Cystosporeae of Leveille ; on the intimate
structure of this, as well as of many other
allied groups, there are as yet but few re-
searches. \Ve have, however, enough in the
beautiful monograph of Cohn, on Pilobolus,
to enable us to discover that it is structurally
more closely allied to the Algae than to the
Fungi. We shall take Pilobolus as an illus-
trative example.
13. Pilobolus has an ephemeral existence.