234 ESSENTIALS OF BOTANY 
a thousand feet. The structure of some of the smaller 
forms is not very unlike that of the pond-scums (Sect. 278), 
while that of the larger ones, as the rockweeds, Fucus 
(Sects. 295, 296), and the kelps is rather complicated. The 
gulf-weed, Sargassum, related to the rockweeds, has ex- 
panded leaf-like branches for photosynthesis, globular air- 
bladders to float the plant, and small branches specialized 
for reproduction. 
In the brown alge the coloring matter appears yellowish 
brown or dark brown; by washing the plants in fresh 
water they soon become green, as the brown pigment is 
dissolved and removed. The reproduction is of various 
types, in the kelps wholly asexual, and in Fucus and its 
allies wholly sexual (Sect. 298). 
RED ALG? 
300. Occurrence. — The red alge are mostly marine and 
many of them are familiarly known as sea-mosses. They 
are especially abundant in the warmer seas, and some of 
them flourish in deeper waters than are frequented by the 
brown alge. 
301. Form and Structure. — Most of the red alge are of 
moderate size, but some genera are minute, almost micro- 
scopic. The simplest forms consist of delicate branching 
threads, each composed of a single row of cells. Others, 
like the so-called Irish moss, appear as rather stout branch- 
ing thalli, and others form broad wavy sheets. Some occur 
as incrustations on rocks or coral. The delicate feathery 
1 No laboratory studies on this group are given since the vegetative char- 
acters are not important for study in a brief course, and the sexual reproduc- 
tion is too complicated to be mastered by beginners in botany. 
