OOSPORES. 



2,yi 



of which contain but little chlorophyll but produce a large number of very small 

 antherozoids (Fig. 177, D) ; 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 {V. pachyderma)] in the V. synandra^ Aiscoxered 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. 





•\<rr 



K 



^^^^H Fig. fj-j. — Vaucheria sessilis ; A,B origin of the antheridium a on tlie branch b, and oogonium og; C an open oogonium 



^^^^H expelling a drop of mucilage si ; D antherozoids ; E the antherozoids collected at the mouth of the oogonium ; /=", a an empty 

 ^^^B antheridium ; osp the oospore in the oogonium (A, B, E, F from nature, C, D after Pringsheim). 



^Hand is completed the next morning ; fertilisation is accomplished between ro and 4 

 ^^Kin the day^. 



^^m Closely allied with Vaucheria in the form of their thallus — which is usually a 

 ^^Rmuch-branched filament undivided by septa — are a series of other genera formerly 

 ^^■comprised in the class SiPHONEiE, the mode of sexual reproduction of which is how- 

 ^^Hever at present unknown, if indeed they have any. It cannot therefore yet be affirmed 

 ^^Bwith certainty whether the Siphoneae constitute a natural group. The mode in which 

 ^^Hthe 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 



^^B ^ (Stahl has described a peculiar encysted form of Vaucheria geminata : this has been previously 

 ^oescribed by Kiitzing as a distinct plant under the name Gongrosira dichoioma. (Bot. Zeit., 1879.)] 

 ^ Braun, Verjiingung in der Natur, p. 136 [Ray Soc, Rostafinski and Woronin have detected 



(Bot. Zeit. 1877) the conjugation of zoogonidia in B. gratndatum. The former considers the Botry- 



diacecE allied to PandorinecE and Hydrodiciyece.'] 



