208 



THE 



a zygospore and the sexual condition is that of isogamy. It is 

 interesting to note that these motile cells sometimes germinate 

 without conjugation, just like the zoospores which they resem- 

 ble, a fact which shows that sexuality has not become very 

 firmly established in the simplest of the brown algae and illus- 

 trates, as in Ulotlirix (Sec. 217), the general conditions which are 

 to be expected with the origin of sex in any group of plants. 



236. The kelps. The kelps (order Laminariales), also known 

 as the devil's aprons, are the largest types of the brown algse. 

 Those of the North Atlantic coast have comparatively simple 



FIG. 195. The giant kelp (Macrocystis) 

 Adapted from Hooker and Harvey 



forms (Fig. 194). There is always a stalk (stipe) attached to the 

 rocks by a holdfast consisting of a cluster of strong outgrowths, 

 and the stalk bears a long, leaf-like expansion called the blade. 

 The blades of some kelps are divided lengthwise into segments, 

 as in Laminaria digitata (Fig. 194, B). 



Certain kelps of the Pacific coast are much more complex, 

 consisting of numerous large, leaf-like blades variously arranged 

 on different forms of stems. Some of the stems attain, great 

 lengths. Thus the giant kelp (Macrocystis, Fig. 195) is known 

 on the California coast, where it grows in large beds, to 

 reach a length of one hundred and fifty feet. The sea otter's 

 cabbage (Nereocystis, Fig. 196) frequently has a stem more 

 than one hundred feet long, which is enlarged above into a 



