490 University of Calif omia Puhlications 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, unbrauched, 400-500ju, long ; hairs unknown ; 

 cells of creeping filaments irregular in form, T-Oju, diam., 1-3 times as 

 long as at the margin ; cells of erect filaments 4.5-5jU, diam. at the base 

 and 2-5 times as long, 8-10/x 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, 50-65jti long, 20-24jti 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,ti 

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



Growing on the pneumatocysts of Nereocystis Luetheana. 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. phyllophilum 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 

 peg-like 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 

 A^aries from 150/x to 500/^. Mature gametangia vary from 55jj. to 

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

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

 variable in difi'erent collections. Two or three cells only may meta- 

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



