298 FUNDAMENTALS OF FRUIT PRODUCTION 



Table 37. — Effect of Rapid Fall Early and Late in the Freezing ^s 



(Missouri)." Hence, the "slow" of Tables 36 and 37 is the "fast" of 

 nature. However, it seems quite possible that certain "warm spots" 

 in an orchard may heat considerably during a clear, cold day only to 

 have a very rapid drop in temperature following sunset and that some 

 of the injury attributed to buds "starting growth" during winter is in 

 reality due to a sudden and considerable drop of this kind. Nevertheless, 

 in a large number of cases when wholesale destruction of fruit buds occurs 

 it can be traced to some other cause. 



Trunk Splitting. — Trunk splitting is much more common in forest 

 and shade trees and most of the literature on this type of injury deals 

 with these trees. Nevertheless, it is by no means unknown in fruit 

 trees; instances are on record of fruit trees splitting through the trunk. ^^^ 



Close measurements in Europe have shown that temperatures under 

 the freezing point induce a contraction in the trunks of various forest 

 trees which with long continued freezing reaches the magnitude of an 

 annual ring.^'' Deciduous trees react much more readily than evergreen. 

 The generally accepted view is that a rapid fall of temperature induces 

 a considerable contraction of the bark and outer wood while the inner 

 wood, still at a much higher temperature, does not shrink equally; 

 hence the splitting. The cracks start generally at the bark and proceed 

 radially toward the center of the tree or even beyond. Objection has 

 been raised that clefts extending beyond the center could not be caused 

 in this way but if it be assumed that the center of the tree is already 

 frozen, those who have cut frozen wood and know how easily it splits 

 will have little difficulty in believing that an initial cracking at the 

 periphery may be transmitted beyond the center because of the glassy 

 nature of frozen wood and the pull of the contracting bark. 



