HOW TO KNOW THE SEAWEEDS 



160b Not as above; without sand-penetrating rhizoids from a stoloni- 

 f erous base , 161 



161a Ligulate blades borne in a drooping bunch from the apex of a 

 stiffly erect, heavy stipe 162 



161b Not as above; blades not borne in a drooping bunch 163 



162a Apex of stipe strongly forked. Fig. 205 Eisenia arborea 



Fig. 205. Eisenia arborea 

 Areschoug 



A. A young plant show- 

 ing the beginning of ero- 

 sion of the apex of the 

 primary blade and the de- 

 velopment of the lateral 

 blades from the meriste- 

 matic area at the base of 

 the primary blade, X 

 0.32. 



B. The lower part of an 

 older plant showing how 

 the stipe has elongated 

 and increased in thick- 

 ness while the primary 

 blade has eroded away 

 completely to its base to 

 produce an artificial fork- 

 ing at which the lateral 

 blades arise on either 

 side of the base of the 

 old primary blade, X 

 0.32. 



This is a common plant 

 of low intertidal levels 

 and below on rocky 

 shores of southern Cali- 

 fornia. It is sometimes mistaken for Postelsia because of its habit, but 

 the ranges of these two plants do not overlap. Eisenia is one of the 

 principal components of the "submarine gardens" of Catahna Island, 

 California. 



Figure 205 



155 



