10 The Principles of Fruit-growing. 



trying to fruits because of the strong ana 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 

 cut end of the cion was sealed 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. 385-388. Work done in Michigan. 



