164 Vniro-sity of California Publications in Botany [Vol.8 



among the Isokontae, to coiisidor Derhesiu as a coenocytic genus of 

 the Stephanokontae. For general convenience, however, connected 

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

 leave it in tiic j)lac(' usually assigned to it. 



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

 and Bryohcsia Weber-van Bosse. Of these Derhc»ia alone has been 

 found, thus far, on our coast. 



6. Derbesia Sol. 



Filaments unseptate, or with occasional partitions, multinucleate, 

 simple or branched, with no diiferentiation 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 pj-riform 

 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 famil}', 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 marina Lyngbye and is now known 

 as D. tenuissima (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 Bryohesia 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 50-70^ in diameter 1. D. mariaa fp. 165) 



1. Filaments 100-000/^ in diameter 2. D. Lamourouxii (p. 165) 



