posteisfa 211 



are the expression of a rythmical in- 

 crease in thickness, they may be com- 

 pared with the growth rings of land 

 plants. Such secondary thickening 

 takes place in the holdfast of Pterygo- 

 phora as well as in the stipe. 



Even in the soral areas some ana- 

 tomical differences can be discovered 

 which will serve to individualize the 

 different genera. Thus, in Nereocystis 

 the cuticular lamella, which is thrown 

 off as the epidermal cells prolong them- 

 selves into paraphyses with basal lat- 

 eral spore-sacs, separates in a contin- 

 uous plate and has the appearance of 

 an exceedingly diaphanous membrane. 

 In Pterygophora and Lessonia the cuti- 

 cle under these circumstances becomes 

 separated in the form of caps, one of 

 which surmounts each spore sac and 

 becomes greatly thickened. Differ- 

 ences, too, in the shape and size of 



