The Anatomy and Physiology of Plants 71 



Now, how does the plant get these mineral elements 

 from the soil? In treating of the germination of the bean 

 we have seen that near the pointed root-cap there is a 

 short space covered with velvety hairs. These hairs on 

 the rootlet are the absorbing agents of the plant through 

 which it gets food from the soil. The pointed root-cap 

 we learned is projected through the soil by the increase 

 of cells behind it; and as fast as new root growth is made 

 there is a new belt of root hairs formed as the old ones dry 

 off, so that the roots are always foraging in fresh soil. 

 Since these root hairs are of extremely minute size, though 

 they have been demonstrated to be tubular, they cannot 

 take in any undissolved matter, and hence the food for 

 the plant must be completely dissolved in the soil water. 



There is some evidence, as you saw in an earlier lesson, 

 that the root hairs themselves have a power to hasten the 

 solution of matters in the soil, and they certainly have the 

 power to select from the dissolved plant-food in the soil 

 water the elements they most desire. Thus, one plant 

 will use potash in much larger percentage than another, 

 and another will seek out the phosphorus and nitrogen 

 more largely. No matter how the roots interlace in the 

 forest each tree does its own work and never by any mis- 

 hap takes on the work of another. 



The soil water, laden with the plant food taken in with 

 it, is carried up through the long tubular-shaped cells and 

 the veins of the leaf till it meets the carbon taken in 

 from the air; and then, in the leaf, which is the labora- 

 tor>' of the plant, all the materials that add growth to 

 the plant are formed. The water that rushes up into 

 the trees in the spring is not sap but merely the material 



