CaSLOBLASTE^. 



853 



oosphere immediately begins to secrete a wall of cellulose 

 about itself, and it thus becomes an oospore {F, Fig. 170). 

 According to Pringsheim, the oospore remains for three 

 months in a resting state before germinating ; in the latter 

 process the outer coat of the spore splits, and through the 

 opening a tube grows out which eventually assumes the form 

 and dimensions of the full-grown plant. 



£ 





Fig. 170.— Sexual orpntia of VaucTieria sessilis. A, beginning of the formation of 

 the oogonium (oa) and antheii-'inm (?t) upon the branch ft. ^. later erage of the 

 same, the antheridinm (a) now separated from the main branch (ft) by a transverse par- 

 tition. O. an open oo2:oninm expelling a drop of mncilage. si. D, epermatozoids. M, 

 spermatozoids collected at the mimth of the oogonium, F^ the antheridinm, a, col- 

 lapsed after the escape of the spermiitozoids ; Ofip, the oospore. X about 100, except 

 2), which ismtich more.— C, 2), after Pringsheim, the others after Sachs. 



(a) The formation of zoospores begins in tlie nigUt, they escape in 

 the inorninn;, and the night following they germinate. 



(5) The formation of sexual organs begins in the evening, and is 

 completed the next morning ; fertilization takes place during the day 

 (from 10 A.M. to 4 P.M.). 



(e) Good specimens of VaucJieria may be found clothing the boggy 

 ground about many springs. Tlife bright green mats may be trans- 

 ferred to the aquarium for the study of zoospores ; but for the sexual 

 organs the dingy and dirty looking specimens must be collected. 



