HOW TO KNOW THE SEAWEEDS 



49b Thalli erect; branching varied, 



50 



50a Branching multifarious. Fig. 80 Polysiphonia 



'^^^ 



Figure 80 



Fig. 80. A species of Polysiphonia with four pericentral cells (only two 

 of which are usually visible) and showing some short trichoblasts 

 from the scar-cells. 



Polysiphonia is a very large genus of relatively small and (or) 

 delicate plants of which about 20 species may be encountered along 

 the Pacific Coast and at least as many along the Atlantic. Some have 

 only four pericentral cells like Figure 80, while others have five to 

 many. The plants may be epiphytic or saxicolous and from as much 

 as 30 cm. tall to as little as a few millimeters. See also Fig. 54A. 



50b Branching distichous .51 



51a Percurrent axes clearly developed. Fig. 81 Pterosiphonia 



Fig. 81. Pterosiphonia dendroidea (Mon- 

 tagne) Falkenberg 



A. An erect axis to show the percurrent 

 character and regular, alternate, pinnate 

 branching, X 3.5. B. Detail of a single 

 compound pinna, X 35. This is a com- 

 mon small saxicolous plant along the 

 whole Pacific Coast. Several other species 

 occur from southern California northward, 

 but apparently there are none on the At- 

 lantic Coast. 



Figure 81 



67 



