624 Howe: Structural dimorphism in Galaxaura 



actual cultures should be made under control conditions as has 

 been done by Hoyt* and by Lewisj to demonstrate the alternation 

 of generations in certain other tetraspore-producing algae. This 

 could be done only in tropical or subtropical waters, would 

 probably require months for its accomplishment, and is not likely 

 to be achieved in the immediate future. Meanwhile, however, 

 it seems to the writer that the proof is conclusive that the sug- 

 gested correlation exists, that the "Spissae" and "Cameratae" 

 characters, first accurately pointed out by Kjellman, do not offer 

 a proper basis for subgeneric groupings of species as supposed by 

 him, but merely distinguish the gametophytic and sporophytic 

 phases in the life-cycle of a single species. 



It is well known that differences of habit occur between sexual 

 and tetrasporic plants of certain red algae, as, for example, in 

 species of Griffithsia, but such differences seem to be due largely 

 to the presence of the reproductive organs themselves or to 

 differences in the form of the cells that are rather directly con- 

 cerned with their production. So far as is known to the writer 

 of these notes, there has been no previous record of a case in 

 which there has been alleged to exist any such constant and 

 pronounced dimorphism in the purely vegetative microscopic 

 structure of the sexual and tetrasporic plants in the Rhodophyceae 

 as is here attributed to Galaxaura ohtusata — differences that do 

 not express themselves in general habit, but afford an easy means 

 of distinguishing a tetrasporic from a sexual plant, even though 

 apparently sterile. 



New York Botanical Garden, 

 Bronx Park, New York City 



* Hoyt, W. D. Alternation of generations and sexuality in Dictyota dicholoma. 

 Bot. Gaz. 49: 55-57- 1910. 



t Lewis, I. F. Alternation of generations in certain Florideae. Bot. Gaz. 

 53: 236-242. 1912. 



