Botrydiaeeae 



415 



zoogonidangium when submerged in water and the zoogonidia escape in 

 great numbers from an apical opening (fig. 265 -2). The zoogonidia are small 

 and ovoid in shape, with two chromatophores and two unequal cilia. If 

 the plants are wet, but not submerged, the zoogonidia do not swarm out, 

 but round themselves off as non-motile gonidia, each of which can grow into 

 a new plant. If, on the other hand, the plants become dry, such as when 



Fig. 265. 1 4, Botrydium grunulatum (L.) Grev. 1, vegetative plant ; 2, the escape of zoogonidia ; 

 3, the formation of 'cysts' in the rhizoids; 4, four zoogonidia. <5, Botrydium Wallrothii 

 Kiitz. 1 3 and 5, x about 50; 4, x about 800. (After Kostafinski & Woronin, from Oltrnanns.) 



N.B. The zoogonidia are here depicted with only one ciliuni, but it has been definitely 

 shown that they possess two of unequal length. 



exposed to strong sunshine, the cytoplasm with the nuclei and chromatophores 

 passes down into the rhizoids and there becomes divided up into a number of 

 separate portions which surround themselves with new walls and become 

 ' cysts ' (fig. 265 3). The cysts may develop in more than one way. If 

 submerged in water th.ey form zoogonidia at once ; if placed on damp earth 

 in the light each cyst puts out a rhizoid and develops directly into a new 



