270 
THALLOPHYTES. 
the branching dichotomous; though commencing monopodially, the lateral branches 
often develope sympodially. At the commencement of the period of growth in the 
spring the plants arise from the oospores which have remained dormant through the 
winter, and are at first propagated through several generations in a purely non-sexual 
manner. This is effected either simply by the abstriction of the ends of branches, or by 
very large zoogonidia which escape from the interior of a cell, and are covered by very 
short cilia. Between these two forms the various species of Vaucheria show intermediate 
steps. In tuber osa, for example, branches swell up to a considerable size, become 
detached at the base, and put out at once one or more germinating tubes. In 
V. geminata the end of a branch swells up to an oval shape, its contents become 
separated by a septum, contract, and form a new cell-wall, and the gonidium thus 
formed either becomes free by the decomposition of the mother-cell-wall, or falls off 
along with it, germinating after some days. The gonidia of F. hamata are formed in 
the same way, but are thrown out with a jerk, remain at rest, and germinate 
during the next night. In other species, as V. sessi/ij, sericea, and piloboloides, the 
Fig. 176. — P'ancheria sessilis (X about 30). 
contents of a branch become separated and contract, and force themselves out as 
a zoogonidium through a crevice at the extremity. The motion of the zoogonidia lasts, 
in F. sericea, only for ^ to i§ minutes, but in other cases for hours. The rotation 
begins, in F. sessilis, as I have distinctly seen, during their escape ; and if the opening 
of the mother-cell is too small, the zoogonidium splits into two pieces ; each becomes 
rounded off and again constitutes an entire zoogonidium; the outer one swims away, 
while the inner one remains rotating within the mother-cell. The formation of the 
zoogonidia begins in the night, as is the case with most Algae and Fungi ; they escape in 
the morning, and their germination commences during the day or the next night. 
They put out on germination either only one or two tubes (Fig. 176, C, D), or form at 
the same time a root-like organ of attachment {E, F, w). The oogonia and antheridia 
originate as lateral protuberances from a filament which contains chlorophyll (Fig. 177,^, 
J3), sometimes even on the germinating tube of a zoogonidium. All the species of Faucheria 
are monoecious, and the two kinds of sexual organs are mostly found very near together. 
The antheridia (Fig. 177, ha) are the terminal cells of slenderer branches, the contents 
