PLANT LIFE 



243 



root-hairs (see Fig. 36). The root-hairs have thin walls. 

 These thin walls are pressed closely to the soil grains, and 

 through them the plant absorbs the liquid that it needs. 

 This liquid is the water of the soil, and substances that are 

 dissolved in it. The plant has no organs like ours in which 

 the digestion of solids occurs before they are absorbed. 

 It has to depend upon the water outside its own body 

 to dissolve the substances that it needs to take in. 



The gas-absorbing apparatus is at the opposite end of 

 the plant. Here the leaves stand in the light, and, in 

 the skin of the leaves, usually on the under surface, are 

 thousands of small pores through which air passes freely. 

 Up to these leaves passes the water that the roots take in, 

 and thence it passes out into the air as water vapor. 



The absorbing root-hairs need to be deep in the soil, 

 for there is the water that they absorb. Only deep- 

 rooted corn-plants can keep on growing through a long 

 drought; the shallow-rooted ones soon die. The leaves, 

 on the other hand, to do their work, must be up in the 

 air and the light. 



So we see that there are three great relations with environ- 

 ment that every food-making plant must have if it is to live 

 and grow. These three are the water-relation, the air- 

 relation, and the light-relation. Of these three, the air- 

 relation presents the simplest problem, and the water- 

 relation usually the most difficult. Lack of water kills 

 more plants than all other causes combined. Lack of 

 light also kills many plants. In forests millions of young 

 plants die because they are overshadowed. In dense 

 forests the light problem is more difficult than the water 

 problem. 



Now you can look with the mind's eye at all the green 



