106 The Principles of Fruit-growing. 
net return of not far from one and one-half dollars 
per tree.” 
Some kinds of fruits may be advantageously pro- 
tected by covering them with temporary (or even per- 
manent) screens. This is extensively done in pine- 
apple culture, in which the better varieties are grown 
under lath or slat sheds, for the purpose of protection 
from frost, sun and drought. Small or amateur 
plantations of strawberries, or even of bush-fruits, 
may be easily covered with lath screens when frost is 
feared. 
Adding vapor of water to the air.—The most 
serious frosts usually occur when the air is dry. 
An abundance of watery vapor in the air probably 
tends to check the radiation of the earth’s heat, and 
the evaporation of water has a pronounced influence 
in raising the dew-point. The means of adding 
vapor to the atmosphere are several: Spraying, 
flooding and irrigating, mulching and tilling. <A 
thorough spraying of plants with ordinary cold 
water at nightfall, when a frost is feared, is one of 
the most efficient means of protection from light 
frosts. The machinery which is used in spraying 
for insects and fungi may be used for this purpose. 
Strawberries and other low plants may be wet at 
nightfall by means of a sprinkling cart. Elaborate 
stand-pipe devices, connecting with underground 
pipes, have been used in California to facilitate the 
spraying of orchards.* The flooding of fruit-plan- 
tations to protect the plants from frost is practi- 
* See Galloway, Yearbook, U. S. Dept. Agric. 1895, 156. 
