CONFERVOIDE^ HETEROGAMY 



327 



only two cells, and then one becomes an oogone, the other an antherid. 

 ■.When the number of cells is greater, the oogones and antherids some- 

 times alternate with one another, but this is not always the case. The 

 contents of an oogone break up into several spherical oospheres, each 

 of which is characterised by a hyaline speck or 'receptive spot.' The 

 antherozoids are produced in extraordinarily large numbers by the 

 breaking up of the contents of an antherid which had previously assumed 

 a brownish red colour. They are furnished with two long slender vibra- 

 tile cilia, and enter the oogones through the orifices in the transverse 

 walls already mentioned ; in their passage they go through remarkable 



Fig. 203. — Portion of filament of 

 SphcEroplea. annnlina. Ag. ; 

 upper cell containing oospheres 

 and antherids, lower cell an im- 

 pregnated oosperm ( x 500). 

 (After Cohn.) 



Fig. 204.—^. anmtlina. A, young unicellular plant 

 ( X 900) ; Bt portion of mature filament, showing 

 thick transverse wall and two nuclei, n {x 800). 

 (After Rauwenhoff.) 



changes of form. The fertilised oospore, or oosperm, clothes itself with 

 a thick cuticularised warty membrane, and its contents turn a brick- 

 red colour. It usually hibernates within the oogone in the form of a 

 hypnosperm ; in the spring its contents break up into three or four 

 zoospores, each of which develops into a slender thread consisting- at first 

 of a single fusiform cell which displays no distinction of base and apex, 

 ■ each extremity being elongated into a fiagelliform point; The oosphere 

 may also break up into zoospores without previous impregnation. 



Probably nearly allied to Spheeroplea, but of somewhat uncertain 

 position, is Cylindrocapsa (Reinsch) (Cienkowski, Mel. Biol Acad. 

 St. Petersbourg, 1876, p. 534), the mode of reproduction of which is 



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