THE GREAT GROUPS OF ALGJ2 
251 
feet long, whose stalk develops root-like holdfasts (Fig. 218). 
The largest body is developed by an Antarctic Laminaria 
form, which rises to the surface from a sloping bottom with 
a floating thallus six hundred to nine hundred feet long. 
Other forms rise from the sea bottom like trees, with 
thick trunks, numerous branches, and leaf-like appendages. 
The common Fucus, 
or " rock weed," is rib- 
bon-form and constantly 
branches by forking at 
the tip (Fig. 219). This 
method of branching is 
called dichotomous^ as dis- 
tinct from that in which 
branches are put out 
from the sides of the axis 
(monopodial). The swol- 
len .air-bladders distrib- 
uted throughout the body 
are very conspicuous. 
The most differenti- 
ated thallus is that of 
Sargassum (Fig. 220), or 
" gulf weed," in which 
there are slender branch- 
ing stem-like axes bearing 
lateral members of various 
kinds, some of them like 
ordinary foliage leaves ; 
others are floats or air- 
bladders, which sometimes 
resemble clusters of berries; and other branches bear the 
sex organs. All of these structures are but different regions 
of a branching thallus. Sargassum forms are often torn 
from their anchorage by the waves and carried away from 
the coast by currents, collecting in the great sea eddies 
FIG. 219. Fragment of a common brown 
alga (Fucus), showing the body with 
dichotomous branching and bladder-like 
air-bladders. After LUERSSEN. 
