124 AGRICULTURE ON THE PACIFIC SLOPE 



Spraying or sprinkling with water at nightfall is a 

 very good means of protection. This depends on the 

 fact that moisture in the air prevents the loss of heat 

 and the cooling of the trees and soil. It acts, so to 

 speak, as a trap for the heat. | Filling the air with dense 

 smoke from smudges of tar, resin, or similar substances 

 serves the same purpose. 



Some kinds of plants stand far more cold than others 

 (just as some kinds stand more water, light, or alkali 

 than others). After a frost which kills most plants, 

 it is often possible to find one or two which have sur- 

 vived, not because of a more sheltered position but by 

 reason of their greater hardiness. By preserving the 

 seed of such plants, and selecting seed from the hardi- 

 est plants year after year, hardy varieties may be ob- * 

 tained. 



