Conservation of soil moisture 



elementary precaution of examining his 

 sub-soil before planting an orchard or a 

 vineyard, and should at the end of five 

 years find his trees a dead loss in con- 

 sequence of an unsuitable sub-soil." 

 Again Hilgard says: "Eastern emi- 

 grants, as well as a large proportion of 

 Californian farmers, do not realize the 

 privileges they possess in having a triple 

 or quadruple acreage of arable soil under 

 their feet, over and above the area for 

 which their title-deeds call." 



Hygroscopic Moisture or Water Vapor. 

 We now come to the third way in 

 which water may occur in a soU. This is 

 as water vapor or hygroscopic moisture.^ 

 The surface-soil absorbs water vapor 

 from the air, and more especially during 

 heavy dews and mists or in cool, damp 



1 If you take a tumbler of cold water into a warm room 

 the glass becomes coated with a thin film of hygroscopic 

 moisture produced by condensation. 



79 



