28 BOTANY 



vous system of man and other large animals, as the ox, elephant, 

 and whale. 



Varying Sizes of Living Things. — Plant cells and animal cells may 

 live alone or they may form collections of cells as tissues. Some plants are so 

 simple in structure as to be formed of only one kind of tissue cells. Usually 

 living organisms are composed of several groups of such tissues. Examples 

 have been given. It is only necessary to call attention to the fact that such 

 collections of tissues may form organisms so tiny as to be barely visible to the 

 eye; as, for instance, some water-loving flowerless plants or many of the tiny 

 animals living in fresh water or salt water, such as the hydra, small worms, 

 and tiny crustaceans. On the other hand, among animals the bulk of 

 the elephant and whale, and among plants the big trees of California, stand 

 out as notable examples. 



Relation to Organic and Inorganic Matter. — The inorganic 

 matter covering the earth, as air and water, and forming the great 

 mass of its bulk, is made use of by plants and animals. The latter 

 make their homes in earth, air, or water ; they breathe the oxygen 

 of the atmosphere; they use the water for drinking; but in the 

 main their food consists of organic matter. Plants, on the other 

 hand, use the elements contained in the soil, air, and water, not 

 only for food, but also to make the living matter of their own 

 bodies. In some mysterious way, of which we shall later learn 

 something, plants take up inorganic and organic substances from 

 the soil and air and transform them into organic matter. This 

 organic matter in turn becomes food for animals. 



In the last chapter we found that the classes of substances in 

 an animal or plant and the organic food substances have a 

 similar composition. Let us now consider chemically the sub- 

 stance which forms the basis of all living things. 



Protoplasm, — Living matter, when analyzed by chemists in the 

 laboratory, seems to have a very com.plex chemical composition. 

 It is somewhat like a proteid in that it always contains the ele- 

 ment nitrogen. It also contains the elements carbon, hydrogen, 

 oxygen, and a little sulphur, and perhaps phosphorus. Calcium, 

 iron, silica, sodium, potassium, and other mineral matters are 

 usually found in very minute quantities in its composition. We 

 believe that the matter out of which plants and animals are 

 formed, although a very complex building material and almost 



