WATER LIFE 207 



only in water, and white oaks only on dry land, but it is 

 seldom that either the water-lily or the oak finds the most 

 congenial place in which to grow. Fine large plants of the lily 

 and strong giant trees of the oak are so infrequent, as com- 

 pared with the whole number, that we stop to admire them. 



358. Originally, plants probably were aquatic, as animals 

 were. Much of the earth was sea. Many plants are now 

 aquatic, and the larger number of these as algae and their 

 kin belong to the lower or older forms of plant life. Many 

 plants of higher organization, however, as the water-lilies, 

 have taken to aquatic life. True aquatic plants are those 

 that always live in water, and that die when the water dries 

 up. They are to be distinguished from those that live on 

 shores or in swamps. Aquatic plants may be wholly im- 

 mersed or under water, or partly emersed or standing above the 

 water. Most flowering aquatic plants come to the surface 

 to expand their flowers or to ripen their fruits. Some aquatic 

 plants are free-swimming, or not attached to the bottom. 

 Of this kind are some utricularias or bladder-worts. In some 

 waters, particularly in the ocean, there are enormous quanti- 

 ties of free-swimming microscopic life, both animal and 

 vegetable, which is carried about by currents: this is known 

 under the general 



name of plankton 

 (Greek for " wander- 

 ing" or "roaming"). 



359. The general 

 tendency has been 

 for plants to become 

 terrestrial, or land-in- 

 habiting. Terrestrial 

 plants often grow in 

 wet places, but never 



in water throughout their entire life; of such are swamp, bog 

 and marsh plants. Some plants have the ability to grow 



