THE WORK OF ROOTS 



119 



drops which are held in the angles between adjacent 

 soil - particles (see Fig. 89, which represents a fairly 

 dry soil) ; it also forms a very thin film on the surface 

 of each particle. The re- 

 maining space is filled 

 with air. 



The water causes the 

 soil -particles to adhere to 

 each other, just as two 

 glass plates do when wet. 

 or the hairs of a brush 

 dipped in water. 



We may picture the 

 relations of the root-hairs 



tO the SOil -particles by 89. Diagram of a fairly dry soil, showing 



, . _ _ -r^. . the relations of a root-hair (rh) to the 



the aid Of Fig. 90, in surrounding soil -particles (sp). The 



which the soil -particles 

 (sp) are represented as 

 surrounded by water, as 

 shown by the contour lines ; this represents a wet 

 soil containing the maximum amount of water in 

 which plants can grow. Here and there air -bubbles 

 (a) occur which furnish the root with oxygen. The 

 root- hairs absorb water whenever they come into con- 

 tact with it ; this causes more water to flow from 

 neighboring particles not actually in contact with the 

 root -hair. In this way each root-hair drains a con- 

 siderable extent of territory. The absorbed water 



water (w^ is held in the form of small 

 drops (menisci) between the angles of 

 adjacent particles; the water also forms 

 a very thin film on the surface of each 

 particle, as well as on the surface of the 

 root-hair. The remaining space is oc- 

 cupied by air (a). 



