PLANTS 



323 



larger than 1/500 of an inch in diameter. The walls are 

 cellulose, a substance which readily permits the passage 

 of fluids through it. These very small roots take the 



FIG. 283. Distribution of Roots. 



food from the soil, while the larger roots carry the food 



to the stem of the tree. 



Stems. - - The main stem of a plant grows in a direction 



opposite to that of the first root of a seed, while the 

 branches from the main stem grow outward 

 in a way quite similar to the root branches 

 .underground. The roots grow in all direc- 

 tions to get food, while the branches from 

 the stems grow outward to get light. 



Experiment 77. Plant some grains of wheat 

 or oats in a box arranged so that the light is re- 

 ceived from but one side (Figure 285). Note the 

 direction of the seedlings as they 'grow. 



Stems serve to hold the leaves in a posi- 

 tion to receive light and air, and they also 

 furnish a pathway for the food-bearing liquid which 

 moves from the roots to the growing parts of the tree. 



FIG. 284. Root 

 Hairs. 



