the buds of our peaches, if they reach a given temperature, 

 they kill regardless of how they thaw. 



The rate at which the temperature falls, however, has much 

 to do with the amount of killing; thus T have been able to 

 kill peach buds at a temperature above zero F. by freezing them 

 very rapidly, and I have been able to kill the tissues of fruit 

 trees in winter at a temperature but 7 degrees below freezing, 

 when with slow freezing they would have stood very much 

 lower temperature. This is of practical importance in several 

 ways. Thus, generally, peach buds will be killed at a tempera- 

 ture of 12 to 15 degrees below zero, if the temperature fall is 

 rather rapid, let us say if the buds have been thawed within 

 twenty-four to forty-eight hours of the time they reach this 

 temperature. A few winters I have had occasion to observe 

 the killing of peach buds when the killing temperature came at 

 the end of a long, cold period. While there had been fluctua- 

 tions in the temperature, the fall had in reality been rather 

 gradual. On such occasions I have known a considerable crop 

 of peaches to be borne on a summer following a temperature of 

 — 24 degrees F. The greater injury following rapid temperature 

 fall is also to be observed in case of sun scald. It is not un- 

 common to see the southwest side of the tree killed. From our 

 studies the explanation of this killing seems to be that on a 

 clear day in winter the temperature on the southwest side may 

 be high enough to thaw the tissue even when the air tempera- 

 ture is nearly zero. As soon as the direct sunlight goes off of 

 that tissue it drops almost instantly to that of the other side 

 of the tree. Then, if the night following is very cold, it is 

 more liable to be killed than if the temperature fall had been 

 more gradual. 



The killing seems to occur on a single cold night rather 

 than as the result of long-continued freezing. This is known 

 to be true in case of buds, for we can thaw them and examine 

 them the next day and find them dead. In case of the wood, 

 if we freeze it artificially, we find that it is killed by tempera- 

 tures about the same as those reached on the extremely cold 

 nights. This may explain why trees are often killed worse in 

 one little section than in another that seems to have about the 



