208 



PRACTICAL BOTANY 



191. The kelps. The giant kelps belong to the brown algse, 

 and are represented by such forms as Laminaria, Postelsia, 

 and Macrocystis. The cylindrical stem-like growth of the 

 Macrocystis is said to reach a length of from 800 to 900 feet, 

 while Laminaria, or " devil' s-apron," grows into strap-like 



or widely spread, 

 tough, leathery 

 expansions. All 

 of these forms 

 have heavy root- 

 like holdfasts, 

 which furnish 

 attachments so 

 strong that the 

 plant usually 

 will break else- 

 where before it 

 will pull away 

 from its sup- 

 port. The great 

 length of these 

 plants is not dis- 

 posed vertically 

 in the water, but 

 the strong stem- 

 like and leaf- 

 like outgrowths 

 trail out in a 

 semi-upright po- 

 sition. 



192. Reproduction. Vegetative reproduction in the brown 

 algse is secured by the breaking apart of branches from old 

 plants. There is no known special method resulting in vege- 

 tative reproduction, as in Pleurococcus, ^Nostoc, etc. 



Some members of the group (Ectocarpus and others) are 

 reproduced by zoospores and by the formation of zygospores 



FIG. 171. Rockweed (Fucus) 



A, the base of a young plant showing an early stage in 

 formation of the holdfast, which attached the plant to a 

 piece of wood. B, tip of a plant; b, air bladders; a, spe- 

 cialized regions in which reproductive organs are formed ; 

 c, new leaf-like growth where the plant had been broken. 

 A little less than natural size 



