38 INTRODUCTION 
disappears, without giving evidence of its nature in dust or 
gases, its body seeming to be a machine which transmutes, but 
does not hold, the substances on which it grows. 
Algze, as has been said above, grow in definite zones, and each 
zone has also a definite animal life which finds there its food. 
Darwin says: “In all parts of the world a rocky and partially 
protected shore perhaps supports in a given space a greater 
number of individual animals than any other station.” And 
speaking of the Laminariacew, he adds: “I can only compare 
these great aquatic forests of the southern hemisphere with the 
terrestrial ones in the intertropical regions. Yet if in any 
country a forest was destroyed I do not believe nearly so many 
species of animals would perish as would here from the destruc- 
tion of the kelp.” The same may be said of the Sargasso Sea, 
where millions of living creatures make their home. In every 
kind of marine fauna there are species which derive, if not the 
whole, at least a part of their nourishment from the seaweeds. 
The vegetation in the narrow boundary of the three zones is 
palpably inadequate to supply the needs of the animal life which 
exists in deeper waters. But over the broad area of the ocean 
there exists a vast number of pelagic, free-floating alge, which, 
although microscopical in size, are almost infinite in numbers. 
In illustration of this it has been estimated that, although they 
are not especially numerous in the Sargasso Sea, yet if all the 
seaweed there were gathered into one mass and the free-floating 
alga into another, the bulk of the latter would exceed that of the 
former. The pelagic flora consists of Diatomacec, Protococcacee, 
Peridiniew, and others. Undoubtedly it is on these pastures that 
fishes feed, as well as other organisms which in turn are food for 
fishes. 
Fucus and Laminaria constitute the kelp from which iodine is 
obtained, and were at one time the source of the potash of com- 
merce. Fucus vesiculosus is a constituent of a medicine used as a 
cure for obesity. Chondrus crispus, commonly known as Irish 
moss, was a few years ago generally used as an article of diet. 
Porphyra vulgaris (laver) is used by the Chinese for soups. Rho- 
dymenia palmata (dulse) is an article of food in Ireland and Scot- 
