HOW TO KNOW THE SEAWEEDS 



55a Thallus greenish 57 



55b Thallus reddish or purplish 56 



56a Thallus mono- to distromatic throughout, purplish; growth inter- 

 calary; reproductive structures in marginal areas, not forming 

 spots. Fig. 86 PoTphyra 



Figure 86 



Fig. 86. Porphyra perforata J. Agardh 



An entire small plant to show the ruffled character resulting from 

 intercalary growth of the membranous blade, X 0.75. This monostro- 

 matic species is common on middle intertidal rocks along the whole 

 Pacific Coast. It is an edible species similar to the porphyras cultivated 

 for food in Japan. It has been extensively harvested in some parts of 

 CaUfornia, as much as 300,000 dry pounds being collected in a year. 

 Several other species of the genus occur as epiphytes or on rocks 

 along the Pacific and Atlantic coasts but must be identified specifically 

 by means of the various local floras. 



70 



