PLANT ROOTS 



183 



variety of different parts. But some plants, like the sea- 

 weeds, appear to have no roots ; some, like the dandelion, 

 no plant stem, and some, like the 

 cactus, no leaves. 



If we dig around the base of a tree, 

 we find in the soil a network of roots 

 holding firmly erect a pillar-like stem 

 with branches bearing a profusion of 

 leaves. If we examine these divisions 

 carefully, we shall find that each has 

 a distinct part to play in the life work 

 of the tree. We shall also find (1) that 

 plants as well as animals need air, water 

 and other kinds of food, (2) that plants, 

 like animals, take in, digest and as- 

 similate food, and (3) that each in the 

 higher forms has parts which are par- 

 ticularly adapted for doing these differ- 

 ent kinds of work. 



92. Plant Roots. Plant roots not 

 only usually secure the plant to the 

 ground so that the stem may be sup- 

 ported, but they take up food from the 

 soil and pass it on to the rest of the 

 plant. In most plants all the foods 

 except carbon and oxygen are taken in 

 by the roots. The soil elements that 

 the plants must have are nitrogen, 

 potassium, calcium, magnesium, phosphorus, sulphur 

 and iron. Water is composed of hydrogen and oxygen, 

 while carbon, the other necessary element, is taken 

 from the air. The soil elements must be in soluble 

 chemical combinations, such as nitrates, phosphates, sul- 

 phates and so on. 



A TYPICAL PLANT. 



Showing root, stem. 



leaf and flower. 



