28o 
THALLOPHYTES. 
out of which proceed very small male plants (dwarf males). Several generative cycles 
or only one may be completed in a vegetative period. The zoogonidium is formed in 
an ordinary cell of the filament (sometimes even in the first cell, Fig. 182, J?) by the 
contraction of its whole protoplasmic substance ; it becomes free from the mother- 
cell, the cell-wall splitting by a transverse slit into two very unequal halves (as in the 
division of the cells) (Fig. 182, j4,B,E). It is at first surrounded by a hyaline mem- 
brane, which however it also breaks through. At its hyaline end — the anterior end 
during the swarming — it is encircled by a circlet of numerous cilia. This end lies 
laterally in the mother-cell, and, after the movement ends, becomes the lower attached 
end which grows out into a rhizoid ; the direction of growth of the new plant is thus 
at right angles to that of the mother-cell. The antherozoids are very similar in form to 
the zoogonidia, but much smaller (Fig. 183, D, 2); their motion, due to a circlet of 
cilia, is also similar. The mother-cells of the antherozoids are cells of the filament, 
but shorter and not so rich in chlorophyll as the vegetative cells ; they lie either 
singly or in groups (sometimes as many as twelve) above one another. In most species 
each antheridium-cell divides into two equal special mother-cells, each of which produces 
an antherozoid ; they escape by the splitting of the mother-cell (as in the case of the 
zoogonidia) (Fig. 183, D). The androgonidia from which the dwarf male plants arise 
are produced from mother-cells similar to those which give birth to the antherozoids 
(without formation of special mother-cells). After swarming they fix themselves to a 
definite part of the female plant, on or near the oogonium, and after germination produce 
at once the antheridium-cells, and in them the antherozoids (Fig. 183, A, B, m, m). The 
oogonium is always developed from the upper daughter-cell of a vegetative cell of the 
filament which has just divided, and immediately after the division swells up into a 
spherical or ovoid form. In Bulbochsete the oogonium is always the lowest cell of a 
fertile branch. This is not opposed to the law of growth above-mentioned, inasmuch as 
the mother-cell of a branch fulfils at the same time the function of its basal cell ; the 
oogonium of Bulbochxte is never the first cell of a branch, since this is always developed 
as a bristle. The oogonium becomes at first more completely filled with contents 
than the remaining cells ; immediately before fertilisation the protoplasm contracts and 
forms, as in Vaucheria, the oosphere, in the interior of which the chlorophyll granules 
are densely crowded. The part of the oosphere which faces the opening of the 
oogonium consists simply of hyaline protoplasm. The opening of the oogonium is 
produced in a variety of ways. In some species of CEdogonium and all of Bulbochsete its 
wall has an oval hole in its side, out of which the colourless part of the oosphere 
protrudes in the form of papillae, and takes up the antherozoids. In some species of 
CEdogonium (Fig. 183, A, B), on the other hand, the oogonium-cell splits, as when the 
zoogonidia are escaping ; and the otherwise straight row of cells of the filament thus 
appears as if broken at this spot. In the lateral fissure appears some colourless muci- 
lage, which the observer can actually see take the form of an open beak-like canal (Fig. 
183, B, %), through which the antherozoid enters. The antherozoid coalesces with the 
hyaline part of the protoplasm of the oosphere and disappears^. Immediately after 
fertilisation the oosphere surrounds itself with a membrane, which afterwards, like its 
contents, assumes a brown colour ; but in Bulbochaete the contents of the oospore thus 
formed is of a beautiful red. The oospore remains enclosed in the membrane of the 
oogonium, which separates from the neighbouring cells of the filament and falls to the 
ground, where the oospore passes its period of rest. When it awakes to new activity, 
the oospore does not itself grow into a new plant ; but in Bulbochsete, where this process 
has been observed, its contents divide into four zoospores, which escape together with 
the inner skin of the oospore, and after this latter is dissolved, swim about. After 
becoming stationary each grows into a new plant. 
^ In O. diplandrum, discovered by Juranyi, the large antherozoids creep in an amoeboid manner 
over the oogonium until they reach the canal, which they slowly enter. 
