THE GREAT GROUPS OF ALGJE 



33 



teristic coast forms. All of them are anchored by holdfasts, 

 which are sometimes highly developed root-like structures ; 

 and the yellow, brown, or olive-green floating 

 bodies are buoyed in the water usually by the 

 aid of floats or air-bladders, which are often 

 very conspicuous. The kelps are most highly 

 developed in the colder waters, and form much 

 of the "wrack," "tangle," etc., of the coasts. 

 The group is well adapted to 

 live exposed to waves and cur- 

 rents with its strong holdfasts, 

 air-bladders, and tough leathery 

 bodies. It is what is known as 

 a specialized group — that is, one 

 which has become highly organ- 

 ized for certain special condi- 

 tions. It is not our 

 purpose to consider 

 such a specialized 

 group in any detail, 

 as it does not usual- 

 ly help to explain the 

 structures of higher 

 groups. 



29. The plant 

 body. — There is very 

 great diversity in the 

 structure of the 

 plant body. Some 

 of them, as Ectocar- 

 pus (Fig. 18), are fll- 

 amentous forms, like 

 the Confervas among 

 the Green Algse, but 

 others are very much more complex. The thallus of Lam- 

 inaria is like a huge floating leaf, frequently nine to ten 



Fig. 18. A browu alga {Ectoearpus), showing a 

 body consisting of a simple filament which puts 

 out branches {A), some sporangia iB) contain- 

 ing zoospores, and gametangia {(' } containing 

 gametes.— Caldwell. 



