372 ANNUAL. REPORT SMITHSONIAN INSTITUTION, 1923 



the year. In the sea the growth of vegetation also varies at different 

 times or seasons quite as much as on the land. 



On land all vegetation grows on the ground, or on some support 

 fixed to the ground, and all animals live on or in the ground or 

 among the plants growing upon it. Such animals as traverse the 

 air do so only as a means of getting from place to place or, a very 

 few, to feed upon others so engaged. The air, for all practical pur- 

 poses, is a sterile medium. Potentially, however, conditions are 

 quite otherwise. 



In the city of Caracas, I was always greatly interested by the 

 sight of festoons of plants, especially " wild pineapples " or 

 bromelias, growing on the electric-light cables high in air and 

 nourished only by substances extracted from the air. What does 

 this signify? It proclaims the fact that wherever a plant can find 

 support it can grow in the air just as well as on the ground, and 

 suggests that if plants could only hover in the air like humming 

 birds the atmosphere in the warmer regions would soon be converted 

 into a dense jungle. Such a calamity is averted by the great weight 

 of plant tissues as compared to air, which forces all plants to grow 

 attached directly or indirectly to the ground. 



Now water is 814 times as heavy as air, almost as heavy as 

 protoplasm, the living substance of which both animals and plants 

 are composed. Only the very slightest modifications are necessary 

 to enable plants and animals to float about suspended at any depth 

 in sea water, like the particles of mud in a muddy river. 



The only plants we see in the ocean are along the shores attached 

 to the rocks, like the devil's aprons or laminarias, the rockweeds, 

 the sea lettuces, etc., or rooted in the mud like the eelgrass. The 

 gulfweed or sargassum, so frequently seen floating in large patches 

 on the north Atlantic, is in reality a rockweed from the Caribbean 

 region growing feebly but never fruiting, and finally dying and 

 going to the bottom, exactly as so many willow twigs would do float- 

 ing on the surface of a lake. 



Quite a number of creatures browse upon these plants along the 

 shores, the largest of these being the manatees when in the sea, the 

 sea cows and the dugongs. But it is obvious that the narrow fringe 

 of seaweeds along the coasts can not supply the food of all the 

 creatures upon which the whales subsist, much less the basic food 

 of the myriads and myriads of other creatures with which the 

 open ocean is populated. It is true that some of the brown seaweeds 

 are very abundant, like the kelps on our New England and our 

 western coasts, and some are of very considerable size, reaching 300, 

 400, or even 700 feet in length; but their actual mass when con- 

 sidered in relation to the food requirements of the sea animals is 

 almost infinitesimal. 



