10 The Principles of Fruit-growing. 
trying to fruits because of the strong and dry 
winter winds, which evaporate the moisture from the 
trees whilst the ground is often so deeply frozen 
that the roots cannot supply moisture. There is 
probably always evaporation from tree tops in win- 
ter when the air is drier than the wood. 
The fact that moisture may be lost from winter 
twigs is a most important consideration in the 
study of the winter injury of trees, and it throws 
light upon the severe damage which often follows 
the “dry freezing” of nursery trees in transit and 
of fall-planted trees. A few figures will show the 
extent to which evaporation may take place through 
the bark of dormant twigs.* 
The extent to which loss of moisture may take 
place through the bark of dormant twigs may be 
determined by cutting off the twigs and quickly 
sealing over the ends with wax, weighing them, and 
then detecting ,the loss in weight from time to 
time. The following figures of such measure- 
ments will serve to emphasize the fact that moisture 
is lost from winter twigs, although they are not 
designed to show the actual rate of this loss when 
the twigs occupy their natural position on the tree. 
April 7, a cion of apple weighing 4.425 grams 
was placed on a balance, and the loss by evapora- 
tion measured at intervals during three days. The 
eut end of the cion was scaled with wax to con- 
fine evaporation to that which may take place 
through the bark. The balance or scales was placed 
* Bailey, Cornell Exp. Sta., Bull. 117, pp. 885-388. Work done in Michigan. 
