6 THE AMERICAN NATURALIST [Vol. XLIII 



holdfast is an almost straight-sided cone 5 mm. in diam- 

 eter and of about equal height. Though apparently in- 

 significant this character makes it easy to pick out Ken- 

 frewia from other kelps while yet very small. So far as 

 the writer is aware it is not present in any other kelp. 



After the plant has reached about a decimeter in length 

 the basal cone ceases to increase and later is lost in the 

 growth of the stipe (Pig. 12). At the same time the disc 

 begins to enlarge and spread out on the substratum, giv- 

 ing a firmer hold for the increasing lamina above. This 

 enlargement is clearly in the region of the primitive disc 

 and not in the conical basal swelling above, which remains 

 part of the stipe. These two tendencies of growth work- 

 ing together usually cause the sharp distinction between 

 the holdfast and stipe to reappear, and in plants more 

 than 15 cm. long the conical base is seldom prominent 

 (Pig. 13). In adults the disc becomes very flat and thin 

 by its continued extension (Fig. 14). 



