Notes on the zygospores of certain New England desmlds 



with descriptions of a few new forms 



Joseph Augustine Cushman 



(With plates 7 and 8) 



While desmids in their ordinary vegetative condition are very 

 common, they are much less frequently found in conjugation. 

 When found in this condition their characters are always worthy 

 of notice. The zygospores of a considerable number of American 

 species have been figured by Wolle and a few by later writers on 

 American desmids, but there are many species of which the zygo- 

 spores are as yet unknown. In many cases the figures given by 

 Wolle have been found inaccurate by later writers. The forma- 

 tion of zygospores, aside from its comparative rarity, is always an 

 interesting process. There appear to be various stages in the for- 

 mation of the spines, as well as other characters, which need more 

 attention to be fully understood. 



A close study of the zygospores of various desmid groups 

 should reveal something concerning relationships and should de- 

 termmc somewhat the validity of one or the other of the two classi- 

 classifications, one based on form alone, the other on arrangement 

 of cell-contents. This should be especially true in the relation- 

 ships of various groups within the genus. On the other hand, 

 certain species, which are almost exactly alike both in external 

 form and structure of contents have zygospores which are widely 

 different in character. Whether such forms should be separated 

 on the basis of differences in the character of their zygospores, 

 representing fruiting conditions, or should be kept close together 

 on the basis of similar form and structure in their vegetative state, 

 is a question to be settled by extended work upon the zygospores 

 of a considerable number of species. 



Whether the zygospores of a single species are always constant 

 in their characters is also somewhat of a question. If they are 



223 



