THE ALGAL 231 
growing places. This is true in the case of Sargassum, some 
species of which thrive along the shores of tropical oceans. 
In the North Atlantic Ocean, north of the Canary Islands, 
is a body of water known as the Sargasso Sea. Its entire 
area is more or less filled with floating Sargassiim and other 
forms of plant and animal life. Sargassum, like some other 
brown alge, is peculiarly fitted 
for floating by the presence 
of “air bladders,” which are 
swollen portions of the leaf-like 
expansions of the plant. In 
mid-ocean one may see small 
floating masses of these plants, 
which have been carried some- 
times hundreds or even thou- 
sands of miles from their original 
homes. 
218. The kelps. The giant 
kelps belong to the brown alge. 
The cylindrical, stem-like plants 
sometimes (as in Mucrocystis) 4, the base of a young plant, showing 
an early stage in formation of the 
reach a length of from 800 to  holdfast, which attached the plant 
900 feet, while “ devil’s apron,” to apiece of wood. B, tip of a plant; 
> : ‘ b, air bladders; u, specialized re- 
(Laminaria) grows into strap- gions in which reproductive organs 
like or widely spread, tough, are formed; c, new leaf-like growth 
: where the plant has been broken. 
leathery expansions. All of A little less than natural size 
these forms have heavy, root- 
like holdfasts, which are so strong that the plant will usually 
break elsewhere before it will pull away from its support. 
At one time the world’s supply of iodine was derived from 
the brown alge ; now it can usually be prepared more eco- 
nomically by chemical means. Soda was formerly secured 
from these plants, but chemical processes have driven out the 
laborious methods of securing that substance directly from 
plants. Gelatinous foods and a sugar known as mannite are 
secured from some species of brown alge. In some coastal 
Fic. 180. Rockweed (Fucus) 
