TEANSPIRATION AND SOIL SOLUTION 



181 



is increased greatly; but when alkalies of any kind 

 are added, transpiration decreases. This is of special 

 interest in the development of dry-farming, since 

 dry-farm soils, as a rule, contain more substances 



Fig. 43 



Ideal tilth of soil. 



that may be classed as alkalies than do soils main- 

 tained under humid conditions. Sour soils are 

 very characteristic of districts where the rainfall is 

 abundant ; the vegetation growing on such soils tran- 



