486 University of California Publications in Botaiui [Vol.8 



Hecatonema diffusum Kylin cf. Cotton, Inc. cit.), at least the two 

 sets of plants agree very closely in general habit and structure as 

 described by Bcirgesen. Judging alone from the description and 

 figures the chief differences are that our plant has short penetrating 

 rhizoids, many terminal and no lateral hairs, and larger gametangia. 

 We are unable to say that the plant would produce rhizoids on an 

 uninjured host. The surface cells of the host are destroyed under the 

 epiphyte, and it is an open question whether the penetrating rhizoids 

 are or are not the cause of their death. Borgesen does not give the 

 dimensions of the whole plant, but he states that the plants form short 

 dense mats on the conceptacles of Himanthalia lore a, which would 

 indicate that they were quite small. Our plants form circular cushions 

 or mats 5-8 mm. in diameter. Typical zoosporangia were found at 

 the base of the erect filaments. The lateral secund gametangia, stand- 

 ing nearly perpendicular to the filaments, the cells of which become 

 the basal part of the gametangia, is a character not found in Comp- 

 sonema gracile Kuckuck. 



17. Compsonema ramulosum S. and G. 



Fronds forming circular cushions 5-7 mm. diam. ; prostrate por- 

 tion monostromatic, composed of more or less contorted and irregularly 

 branched radiating filaments; erect filaments piliferous in part, 

 unbranched or bearing above short, mostly fructiferous and secund 

 branches and occasional hairs, tapering slightly at the base ; cells of 

 creeping filaments 6-7/* diam., quadrate or slightly longer than the 

 diameter ; cells of erect filaments 6-7. 5/x, diam. at the base, slightly 

 broader above, 1-3.5 times as long ; cells of the branches and hairs 

 4-6/* diam. ; chromatophores band-shaped, more or less broken and 

 angular; zoosporangia (?) broadly clavate, terminal on longer or 

 shorter pedicels, lateral and secund or whorled near the ends of the 

 erect filaments; gametangia exceedingly variable in shape, size and 

 position, sessile or pedicellate on the creeping filaments or lateral on 

 the erect filaments or intercalary or terminal either on short lateral 

 ramuli or on the main filaments, clavate, cylindrical to cylindrico- 

 conical, up to 140/*, long, 16/* broad, loculi mostly 2-seriate. 



Growing on the pneumatocysts of Nereocystis Luetkeana. Carmel 

 Bay, Monterey County, California. 



Setchell and Gardner, Phyc. Cont, III, 1922, p. 362, pi. 39, figs. 1-5. 



There exists in this species extreme variation in the form, size, and 

 position of the gametangia. Some are sessile on the creeping filaments, 





