54 



THE VEGETATIVE FUNCTIONS OF PLANTS 



49. Relation between the Water and the Soil. Fig. 

 43 is a diagram, showing on a greatly enlarged scale, 

 how the root-hairs lie in the soil, and the condition of the 

 soil most desirable for the well-being of the plant. It 

 is seen from the figure that the soil is not compact, but 

 open or porous, the soil particles being separated by 

 spaces as large or larger than themselves. Under con- 

 ditions most favorable for the plant, the spaces are 



FIG. 43. Diagram to illustrate a root-hair (K) in the soil, and its 

 relation to the soil-particles, the capillary film of water (w), and the air 

 spaces (a); e, epidermal cell of the root, of which the root-hair is an out- 

 growth, or branch. (After Sachs.) 



filled with air, while each particle of soil is surrounded by a 

 thin film of water. This is the water that supplies the 

 plant through the root-hairs. As fast as removed it is 

 replenished by the capillary action of the soil. Roots 

 will continue to remove the capillary water from the soil 

 until a point is reached where the attraction of the soil- 

 particles for the water exceeds the absorbing power of the 

 root-hairs; then the plant will wilt unless more water is 

 added. Plants cannot absorb all the water from the soil. 



