62 CHLOROPHYCEAE 



haploid. In one species it has been definitely established that two 

 of the zygote segments ultimately develop into male plants and two 

 into female plants. Zygote germination without meiosis is not 

 uncommon, in which case it gives rise to what are presumably 

 large diploid swarmers, and these develop into abnormally large 

 threads that are always female. Oogonia appear on these diploid 

 filaments and can be fertilized, but the fate of the zygote is un- 

 known. 



It remains to discuss the possible origin of the androspores, and 

 there are two hypotheses that may be considered : 



(a) The androspore is equivalent to the second and smaller type 

 of asexual zoospore, such as those found in Ulothrix, but in the 

 Oedogoniales tliey can no longer give rise to normal filaments. On 

 this view the nannandrous forms are the more primitive, the 

 macrandrous having been derived by the androsporangium ac- 

 quiring the capacity to produce antheridia immediately and hence 

 never appearing, (b) The androspore is equivalent to a prematurely 

 liberated antheridial mother cell which subsequently undergoes 

 further development. On this view the macrandrous species are 

 the more primitive. West (191 2) considered that the dwarf males 

 were to be regarded as reduced from normal male filaments, for in 

 one species the male plants are intermediate in size. At present 

 there does not appear to be any ver>^ convincing evidence in support 

 of either theory, 



REFERENCES 



GussEWA, K. (1931)- Planta, 12, 293. 

 Mainx, F. (1931)- Z' Bot- 24, 481. 

 OHAsm, H. (1930)- Bot. Gaz. 90, 177. 

 Spessard, E. a. (1930). Bot. Gaz. 89, 385. 

 West, G. S. (1912). jf. Bot, 50, 321. 



