The Anatomy and Physiology of Plants 73 



Some green-leaved plants grow immersed in water, and 



these get their carbon from the air always present in water 



and in turn they keep the water supplied with oxygen to 



support aquatic life in animals that live in the water. 



Put a few fish in a vessel of water, and they soon exhaust 



the oxygen and are found sucking air at the surface and 



soon die. But if a few water plants are grown in the vessel 



where the fish are they remain healthy and thrive. This 



shows that water always contains some air, and that plants 



are essential to animal Hfe in water as on land. Without 



plants there could be no Hfe either on land or in the water, 



for plants use the minerals which animals cannot use and 



transform them into shapes that are the food of animals. 



On the other hand, a large part of the food of animals is 



excreted and returned to the soil for the use of plants, and 



the dead bodies of animals return to the earth to feed 



other plants, thus keeping up the round of nature. 



Plants are increased in various ways. 



How Plants The natural way in which all of our higher 



Are Perpetu- pj^j^^s are increased is by the seed. In the 

 ated and ^ , , , . . , ^, 



Perfected blossoms of plants the leaves, which on other 



parts of the plant perform the work of taking 



in carbon, are transformed into the various organs, each 



having its special office to perform in perpetuating the life 



of the plant. 



The normal, complete, and perfect flower has four sets 



of organs. First, at the end of the stem bearing the flower 



we find what is called the calyx of the flower. This is 



commonly green, but sometimes colored (botanists do 



not class green as a color, it being the natural color of 



plants, and when a part is said to be colored it means 



