258 IP s te I s i a 



whether the two can be separated for there is 

 no anatomical character and the texture which 

 usually comes to one's assistance in such cases, 

 is not sufficiently different to form a basis of 

 separation. Tlie only other kelp whose juve- 

 nile forms are likely to be confused with those 

 (jf the present species is C yniatJicre tripUcata 

 which is similar to this in structure of the hold- 

 fast, a character which separates them from 

 most other kelps when still very young. But 

 in C ymathcvc the lamina is much narrower 

 and thinner and the folds begin to a{)pear 

 when they are 2-3 centimeters in length. 



Histology. The thallus of Rcnjreixna is 

 composed in general of the same tissues as 

 the other kel})s. The central portion of the 

 body is composed of ])ith-web sharply delimi- 

 ted from the surrounding cortex which exter- 

 iorly shades into the smaller, more active cells 

 of the hypodermis and epidermis. Since the 

 histology of several of the kelps has been so 

 thoroughly worked out by recent investigators, 

 mostly at the Minnesota Seaside Station, it 

 will be unnecessarv to give a detailed account 



