490 University of California Publications in Botany [Vol. 8 



2. Hecatonema variabile S. and G. 



Fronds forming circular cushions, 4-7 mm. diam.; prostrate por- 

 tion composed of regularly radiating filaments with subterminal 

 branching, attached by numerous short rhizoids, 1-3 cells long ; erect 

 filaments not densely crowded, not arising successively from the center 

 toward the periphery, unbranched, 400-500** long; hairs unknown; 

 cells of creeping filaments irregular in form, 7-9/* diam.. 1-3 times as 

 long a.s at the margin; cells of erect filaments 4.5-5/* diam. at the base 

 and 2-5 times as long, 8-10/* diam. and 1-3 times as long toward the 

 distal end; zoosporangia (?) broadly clavate, sessile or on short 

 pedicels on the prostrate filaments, rarely lateral or terminal on the 

 erect filaments, 50-65/* long, 20-24/* broad; gametangia cylindrical, 

 tapering slightly at the apices, sessile or on short pedicels on the 

 prostrate filaments or rarely terminal on the erect filaments, 70-120/* 

 long, 9-12/* broad ; loculi 1-2-seriate. 



Growing on the pneumatocysts of Nereocystis Luetkeana. Carmel 

 Bay, Monterey County, California. 



Setchell and Gardner, Phyc. Cont. IV, 1922, p. 377. pi. 41. figs. 

 1-12. 



From the standpoint of the structure of the gametangia. the type 

 of this species of Hecatonema could scarcely be separated from a 

 Myrionema such as M. phyllophUum S. and G. They, in part, possess 

 uniseriate loculi, but have many perpendicular and slanting walls, 

 making a partial biseriate condition. The basal layer, particularly in 

 the center of the thallus, is distinctly distromatic, developing numerous 

 pegdike rhizoids, which serve to anchor it more firmly to the host, and. 

 for the most part at least, the branching of the filaments is subterminal. 

 whereas that of a true Myrionema is terminal and brought about by 

 the splitting of the apical cell. 



The size of the plants as a whole varies considerably. The material 

 of the type varies in this respect from 4 mm. to 7 mm. in diameter. 

 In some collections of specimens which we have included under the 

 species, the specimens are as small as 2 mm. in diameter, in others 

 they are up to 10 mm. in diameter. The length of the erect filaments 

 varies from 150/*, to 500/*. Mature gametangia vary from 55/* to 

 120/* long. The relative number of gametangia terminal on the 

 erect filaments, as well as their size and complexity, is exceedingly 

 variable in different collections. Two or three cells only may meta- 

 morphose in some filaments, in others eight or ten. Occasionally small 



