164 University of California Puhli oat ions in Botany [Vol. 8 



among the Isokontae, to consider Derhesia as a coenocytic genus of 

 the Stephanokontae. For general convenience, however, connected 

 with the fact that this account deals with marine species only, we 

 leave it in the place usually assigned to it. 



There are only two genera to represent this family, Derhesia Solier 

 and Bryohesia Weber-van Bosse. Of these Derhesia alone has been 

 found, thus far, on our coast. 



6. Derbesia Sol. 



Filaments unseptate, or with occasional partitions, multinucleate, 

 simple or branched, with no differentiation of axis and branches; 

 chromatophores numerous, discoid, with or without pyrenoids; non- 

 sexual reproduction by large, multiciliate, stephanokont zoospores, 

 each with a single nucleus, formed in lateral globose to pyriform 

 zoosporangia ; sexual reproduction unknown. 



Solier, Sur deux alg. zoosp. form, le nouv. genre Derhesia, 1846, 

 p. 453 (cf. also Bot. Zeit., vol. 4, 1846, p. 497), Mem. sur deux algues, 

 1847, p. 158. 



Little remains to be said of the genus Derhesia after the de- 

 scription of the family, since there are only two genera included in 

 Derbesiaceae. The genus Derhesia was founded on D. marina and 

 D. Lamourouxii, of which the former is given first, and may properly 

 be considered as the type. D. marina Solier, however, is judged not 

 to be identical with Vaucheria mariiia Lyngbye and is now known 

 as D. tenuissinm (De Not.) Crouan. The genus at present consists of 

 eight to ten species widely distributed chiefly in tropical and sub- 

 tropical waters. It differs from Bryohesia in having the sporangia ( ?) 

 lateral. In Bryobesia after the terminal sporangium is emptied it is 

 forced to one side by the continued growth of the filament beneath. 



Unfortunately we have had no opportunity of studying any of 

 our Pacific Coast species of Derhesia in the living condition and must 

 draw upon the publications of others for all details. 



Key to the Species 



1. Filaments 50-70m in diameter 1. D. marina (p. 165) 



1. Filaments 100-600ju in diameter 2. D. Lamourouxii (p. 165) 



