HOW TO KNOW THE SEAWEEDS 



77a Branching more or less clearly dichotomous or trichotomous. the 



cells large enough to be visible to the naked eye. Fig. Ill 



Grifiithsia 



Fig. 111. Grifiithsia pacifica Kylin 



A small upper part of a male 

 plant, X 6.4, showing the large 

 cells and dichotomous branching. 

 This is the commonest and most 

 widespread species along the Pa- 

 cific Coast from Puget Sound to 

 southern California. G. globulifera 

 Harvey is common along the At- 

 lantic south of Cape Cod and has 

 cells up to 1.5 mm. in diameter. 

 G. tenuis C. Agardh, with the same 

 range, is 5-20 cm. tall but with 

 slender, elongate cells about 300 

 jji in diameter or less. 



Figure 1 1 1 



77b Branching irregular, unilateral, alternate, or sometimes opposite; 

 cells microscopic. Figs. 109, 112 SpeTmothamnion 



Fig. 112. Spermothamnion snyderae Farlow 



A small portion of a plant bearing poly- 

 sporangia, X 80. This is the only species of 

 the genus occurring along the Pacific Coast. 

 It is a small plant to 5 cm. high growing in 

 dense tufted masses on rocks from central to 

 southern Cahfornia. Unlike the Atlantic S. tur- 

 neri, it has polysporangia. S. humeri, our only 

 Atlantic species, is of similar stature, but is 

 epiphytic. 



Figure 1 1 2 



87 



