CONFERVOWE.^ HETEROGAM.E 



227 



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 

 Spheeroplea ann7ilhia Ag. ; 

 upper cell containing oospheres 

 and antherids, lower cell an im- 

 pregnated oosperm ( x 500). 

 (After Cohn.) 



n 



B 



Fig. 204. — 6". anmdina. A, young unicellular plant 

 (x 900 ; B, portion of mature filament, showing 

 thick transverse wall and two nuclei, « ( 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 uriually hibernates within the oogone in the form of a 

 hypnosperni ; 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 flagelliform point. The oosphere 

 may also break up into zoospores without previous impregnation. 



Probably nearly allied to Sphaeroplea, but of somewhat uncertain 

 position, is Cylmdrocapsa (Reinsch) (Cienkowski, ^lel. Biol. Acad. 

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



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