66 



Table 21. Showing the Relative Effect on the Resistance 



to Low Temperature of Rapid Temperature Fall 



Toward the Beginning and Toward the End 



of the Freezing Period. 



It will be seen that rapid falling in the early part of the freezing 

 period down to -12° C, does more harm than rapid fall in the latter 

 part of the period, from -12° C. to the killing temperature. This 

 rapid freezing probably has considerable to do with the amount of 

 killing at times in nature, though just how much it is difficult to tell. 

 In this investigation it was not possible to cause, the temperature to 

 fall more slowly than the most rapid fall to be observed naturally 

 in the climate of this station. Yet there are probably times when 

 on sunny, cold days the temperature of some tissue may rise to near 

 the freezing point due to the absorption of the heat by the dark color 

 of the bark. In this case when the sun is off the twigs, the tempera- 



