154 



ANIMALS OF LAND AND SEA 



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 in- 

 directly 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 sus- 

 pended 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 hke the devil's aprons or laminarias, the 

 rock-weeds, the sea-lettuces, etc., or rooted in the mud like the 

 eel-grass. The gulf-weed or sargassum, so frequently seen 

 floating in large patches on the north Atlantic, is in reaUty a 

 rock-weed 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 floating 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 sea-weeds along the coasts cannot 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 sea-weeds are very abundant, Hke 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 considered in re- 

 lation to the food requirements of the sea animals is almost 

 infinitesimal. 



On pools and ponds and in quiet backwaters from lakes and 

 rivers in the summer time the water is often quite hidden from 



