EUPHYCOPHYTA 



35 



parent colony, whilst asexual reproduction is secured by means of 

 biflagellate swarmers that may develop into a new colony or into a 

 thick-walled resting spore that later gives rise to a new colony. The 

 sexual colonies are monoecious or dioecious, depending on the 

 species, and give rise to biflagellate isogametes. After fusion the 

 zygote gives rise to four to eight aplanospores that are said to grow 

 into new colonies. Recent work on T. gelatinosa suggests that the 



Fig. 12 Tetraspora. A, T. cylindrica ( x |), B, portion of colony of 



T. cylindrica showing outer envelope ( x 155). C, T. luhrica ( x ^). 



D, portion of colony of T. lubrica ( x 500). (After Smith.) 



aplanospores are not always produced and that the zygote, after a 

 resting period, can give rise directly to a new plant. In T. gelatinosa 

 the new plant must be diploid and it gives rise to asexual swarmers. 

 These develop into juvenile colonies that are capable of perpetuat- 

 ing themselves by biflagellate swarmers. Eventually swarmers are 

 produced that give rise to an attached, pear-shaped colony. The 

 swarmers from this colony give rise to the sexual plant so that in 

 this species there is a definite alternation of morphological phases 

 (Fig. 13). The place of meiosis does not yet appear to have been 



