16 The Principles of Fruit-growing. 



"In observing trees in continuous severe winter 

 weather, ray attention has often been called to the 

 fact that the twigs seem somewhat duller and more 

 somber than usual, and in some cases tend to shrivel 

 up and have the appearance of drying out. When 

 a warm spell comes, this condition changes, and the 

 twigs become brighter and seem to freshen up, and 

 sometimes I imagine that they become more plump. 

 The freshening -up feature is especially noticeable on 

 large clumps or groves of willow; the twigs usually 

 take on a much brighter color during warm spells 

 in winter than during the continued freezing weather. 

 During thawing weather, the equilibrium is main- 

 tained between the moisture or sap in the tree top 

 and that taken in by the roots, and as fast as mois- 

 ture evaporates from the tree top, sap flows up from 

 the roots and the equilibrium is re-established. In 

 freezing weather, the moisture, even though frozen, 

 is probably evaporating from the tree tops ; and 

 the sap, being frozen, does not flow up from the 

 roots and replace the evaporated moisture. Thus 

 the equilibrium between the tree tops and roots is 

 unbalanced, and it is at this time that the twigs 

 become shriveled by reason of moisture being lost 

 and not replaced. 



"In support of these statements, I made the fol- 

 lowing investigation: After several days of con- 

 tinuous freezing weather, and at a time when I 

 expected a thaw, I cut twigs of a variety of trees 

 and estimated the percentage of moisture contained 

 in them. Again, just as soon as a thaw came, I cut 



