Killing of Plant Tissue by Low Temperature 203 



but there was so little apparent difference between the results that 

 the data are not given. The killing temperature lies so near the 

 freezing point that possibly the slowly frozen tissue kills badly be- 

 cause it is exposed to temperatures around the killing point longer. 

 This tender tissue was exposed to the minimum temperature for 

 from twenty to thirty minutes. 



It will be seen that the rate of temperature fall with winter 

 twigs and buds exerts the greatest influence on the extent of killing 

 at a given temperature of any feature we have so far discussed. 

 And in the case of very forward, rather tender fruit buds, the rate 

 of temperature fall exerts great influence. Thus on March 24, 1913, 

 when all buds, especially of peaches, plums and cherries, had made 

 much growth, a temperature of -11.5 C. killed as many buds with 

 rapid temperature fall as a temperature of -16.5 C. with a slower 

 temperature fall. 



Tests were made to see whether the rapid temperature fall 

 that does the most harm is in the early part of the ice forming state, 

 or in the later part. The following table gives the results with peach 

 buds frozen slowly one-half way down to the killling temperature 

 and rapidly the remainder of the way, and others frozen rapidly one- 

 half the way down and slowly the remainder of the way, and others 

 slowly all the way down : 



