HOW TO KNOW THE SEAWEEDS 

 101b Vesicles not distichous 102 



102a Vesicles borne in series 103 



i02b Vesicles solitary 104 



103a Seriate vesicles compressed. Fig. 137 Halidrys dioica 





v:^>'^^?^ -^k.. A>^iw^- 



Figure 137 



Fig. 137. Halidrys dioica Gardner 



A single series of vesicles showing the flattened character, X 1.8. 

 Note that some forms may have a less pronounced blade-like develop- 

 ment than is shown in the figure. 



Halidrys is vegetatively similar to Cystoseira (See Fig. 138) and 

 may be confused with members of that genus in the absence of the 

 readily recognizable vesicles. The only species, H. dioica, is restricted 

 to southern Cahfornia, while species of Cystoseira extend farther north. 



103b Seriate vesicles spherical and catenate. Fig. 138 Cystoseira 



Fig. 138. Cystoseira osmundacea (Menzies) C. Agardh 



Habit of a short, intertidal form of this species to show the hold- 

 fast, leaf-Hke blades, and catenate vesicles, X 0.5. This is the most 

 widespread of three species of this genus on our Pacific Coast, ex- 

 tending throughout CaHfornia to central Oregon. Many plants, espe- 

 cially infratidal ones, are much more lax in habit than the plant illus- 

 trated. Central California plants are reported to reach a length of 7.5 

 meters. Entangled pieces of Cystoseira are often found in drift along 

 California beaches. 



106 



