;,0(i University of California Publications in Botany [Vol. 8 



Typically, however, in the mature stages of the two genera, Elaehistea 

 has a firm, closely intertwined, agglutinated mass of filaments for the 

 basal port ion, and Gonodia remains free and loosely intertwined. We 

 are using this character as a basis of separating the two genera. 



Key to the Species 



1. Basal cells of the erect free filaments symmetrical 1. G. Johnstonii (p. 506) 



1. Basal cells of the erect free filaments asymmetrical... 2. G. Marchantae (p. 506) 



1. Gonodia Johnstonii S. and G. 



Plants forming dense minute tufts in the conceptacles and on other 

 parts of the host, 160-200/* high, attached by rather deeply penetrat- 

 ing, sparsely branched, rhizoidal filaments; erect fronds forked at the 

 surface of the host, vegetative filaments unbranched above, decidedly 

 clavate and blunt, at times tapering upwards above the center ; cells 

 in widest part 10-14/* diam., 1-1.5 times as long as broad, slightly 

 constricted at the dissepiments; zoosporangia broadly clavate, 65-75/* 

 long, 18-22/1 broad ; gametangia cylindrical, 60-75/* long, 6-9/* broad, 

 densely fasciculate ; both sets of reproductive organs borne on the same 

 plant at the surface of the host. 



Growing on Sargasswm msulare. San Marcos Island, Gulf of 

 California. 



Setchell and Gardner, Mar. Alg. Gulf Calif., 1924, p. 722, pi. 17, 

 figs. 46, 47. 



*to K 



2. Gonodia Marchantae S. and G. 



Fronds forming dense tufts with a dense mass of colorless filaments 

 at the base penetrating the host, the free portion about 200/* long ; fila- 

 ments unbranched above the host, the lower portion composed of 2-3 

 long, narrow cells, abruptly changing into 2-3 asymmetrical swollen 

 cells, then gradually attenuated upwards to blunt apices; widest cells 

 18-22/*, the length of the cells in the upper part equaling the breadth ; 

 pseudoparenchymatous cells doliiform to subspherical ; zoosporangia 

 broadly clavate, 55-65/* long, 22-26/* broad; gametangia cylindrical, 

 densely fasciculate 55-65/* long, 6-7/* broad ; both sets of reproductive 

 organs borne on the same plant at the base of the free filaments. 



Growing on the fronds of Sargassum horridum. La Paz, Lower 

 ( lalifornia. 



Setchell and Gardner, Mar. Alg. Gulf Calif., 1924, p. 723, pi. 17, 

 fig. 48. 



