230 SEA AND LAND 



The part played by vegetable life in the organic economy of 

 the seas is quite as important as is its rcMe upon the land. In 

 both realms the plants act as mediators between the mineral 

 kingdom and the higher animal life, which exists solely by 

 means of the mineral elements that the vetjetation has brought 

 into a state where animals can make it useful in maintaining 

 their functions. In the seas plant life appears to be almost 

 altogether limited to shallow water next the shores, or to super- 

 ficial parts of the open ocean. Except in the case of the vast 

 growths of gulf weed which exist in the central parts of the 

 north and south Atlantic and Pacific oceans and the abundant 

 diatoms which develop, particularly in high latitudes far from 

 the land, almost all the vesfetable life of the ocean erows near 

 the shores in less than a hundred feet of water. The fact is 

 that vegetable life generally demands^^lie liglit> and with few 

 exceptions is not known to develop in marine waters below the 

 level which has some share of the sun's rays. Only one species, 

 the giant kelp of the Pacific, is known to fasten itself to the 

 bottom at depths of two hundred feet or more, and this unique 

 form elevates its fronds to the surface of the water on a mar- 

 vellously long and strong stalk. 



The species of plants the growth of which is favored by 

 salt water belong to two great groups — the algae or seaweeds, 

 that have no true roots or flowers and otherwise possess only 

 a lowly organization, and flowering plants that have adapted 

 themselves in an exceptional way to the conditions which a 

 station in salt water imposes. In general the seaweeds are 

 most common in more open water than harbors aflbrd, and the 

 larger part of their species grow only below low-tide mark. 

 The higher flowering plants which live in the sea water rarely 

 meet with fit conditions for nurture beyond the limits of the 



