OOSPORES. 
of which contain but little chlorophyll but produce a large number of very small 
antherozoids (Fig. 177, i)) ; these escape from the antheridial cell which bursts at 
the apex. In several species the antheridia are curved like horns; in others they are 
straight {F. sericea) or curved sacs {F. pachyderma) ; in the V. synandra, discovered by 
Woronin, from two to seven small horns arise on the large ovoid terminal cell of a two- 
celled branch. The oogonia arise as thick protuberances (Fig. 177, A, B, og) filled 
with oil and chlorophyll. They swell up into an obliquely ovoid form, and finally the 
dense contents are separated by a septum (F, osp). The green and coarsely granular 
"mass collects in the centre of the oogonium, while colourless protoplasm accumulates 
at its apex, at which spot it opens; at this moment the whole contents contract 
and form the oosphere. In some species a colourless drop of mucilage is expelled 
from the mouth. After the entrance of the antherozoids the oosphere clothes itself with 
a thick cell-wall ; its contents become red or brown, and the oospore now commences 
its period of rest. The formation of the oogonia and antheridia begins in the evening, 
Fig. \T]. — Vaucheria sessilis ; A,B origin of the antheridium a on the branch b, and oogonium og; C an open oogonium 
expelling a drop of mucilage si ; D antherozoids ; E the antherozoids collected at the mouth of the oogonium ; F, a an empty 
antheridium ; osp the oospore in the oogonium (A, B, E, F from nature, C, D after Pringsheim). 
and is completed the next morning; fertilisation is accomplished between 10 and 4 
in the day^. 
Closely allied with Faucheria in the form of their thallus— which is usually a 
much-branched filament undivided by septa— are a series of other genera formerly 
comprised in the class Siphoned, the mode of sexual reproduction of which is how- 
ever at present unknown, if indeed they have any. It cannot therefore yet be affirmed 
with certainty whether the Siphonese constitute a natural group. The mode in which 
the gonidia are formed is at least not opposed to this idea. The following forms may be 
especially mentioned :— In Botrydium ^ the young plant is a spherical cell, from which 
^ [Stahl has described a peculiar encysted form of Vaucheria gemmata : this has been previously 
described by Kützing as a distinct plant under the naiTie Gongrosim dichotoma. (Bot. Zeit., 1879.)] 
2 Braun, Verjüngung in der Natur, p. 136 [Ray Soc. Rostafinski and Woronin have detected 
(Bot. Zeit. 1877) the conjugation of zoogonidia in B. gramdatum. The former considers the Botry- 
diacecB allied to Pandoriiiece and Hydrodictyece.^ 
