THE GREAT GROUPS OF ALG^E 
249 
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. 
170. The plant 
body. There is very 
great diversity in the 
structure of the 
plant body. Some 
of them, as Ectocar- 
pus (Fig. 217), 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. 217. 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. 
