THE GREAT GROUPS OF ALGM 



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. Certain Brown Algae, as 

 Ectocarpus (Fig. 18), are of great 

 interest on account of their pos- 

 sible relation to the evolution of 

 higher plants. It is 

 in this group that we 

 have found our only 

 suggestions as to the 

 origin of the complex 

 sex-organs occurring 

 in Bryophytes and 

 Pteridophytes. 



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. — Caldwell. 



