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 fil- 

 amentous forms, like 

 the Confervas among 

 the Green Algae, 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 brown alga (Ectocarpus), showing a 

 body consisting of a simple filament which puts 

 out branches (A), some sporangia (B) contain- 

 ing zoospores, and gametangia (C) containing 

 gametes. CALD WELL. 



