WINTER KILLING AND HARDINESS 261 



Winkler, 217 working with dormant twigs that killed at — 22°C. upon rapid 

 freezing, found that by small successive reductions of temperature, at — 16°C. 

 for 3 days, at -18°C. for 2 days, at -20°C. for 3 days, at -22°C. for 2 days, 

 at — 25°C. for 3 days, the twigs were enabled to withstand 12 hours of freezing 

 at from — 30°C. to — 32°C. Chandler^** reports on the results of his work, 

 in part, as follows: "The rate of temperature fall is very important indeed, 

 especially in case of winter buds. In fact apple buds can be frozen in a 

 chamber surrounded by salt and ice rapidly enough that practically all of them 

 will be killed at a temperature of zero F., or slightly below, while it is well known 

 that they may go through a temperature of 20°F. to 30°F. below zero with but 

 slight injury where the temperature fall is not so rapid . . . the killing tem- 

 perature of rapidly frozen twigs was four and a half degrees higher than that 

 of the more slowly frozen twigs, and even then the buds of the rapidly frozen 

 twigs killed the worst, . . . rapid falling in the early part of the freezing 

 temperature down to — 12°C., does more harm than rapid fall in the latter part 

 of the period, from — 12°C. to the killing temperature." "Many young fruits 

 and succulent plants were also frozen slowly and rapidly but there was so little 

 apparent difference betAveen 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 because it is exposed to temperatures around the killing point 

 longer." "... the rate of temperature fall with winter twigs and buds ex- 

 erts 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 the peaches, plums and cherries, had made 

 much growth, a temperature of — 11.5°C. killed as many buds with rapid tem- 

 perature fall as a temperature of — 16.5°C. with a slower temperature fall." 



A factor involved in very rapid lowering of the temperature is the 

 possibility of ice formation within the cells. Though the rate of tem- 

 perature fall involved probably does not occur in nature, it may have 

 been produced in some of the experiments just described. 



Slow and Rapid Thawing. — Practical men have long held that rapid 

 thawing intensifies damage from low temperatures and many investi- 

 gators have accepted this view. The fruit grower who heats his orchard 

 during the cold nights of the growing season tries just as carefully to 

 keep the early morning sun from the blossoms; the young florist is taught 

 by older men to supply heat very slowly if accident has lowered the 

 temperature of the greenhouse to a critical point. 



Wiegand^i* found that thawing generally occurs at temperatures 

 below 0°C., or about at the freezing point (-3.5°C. to -2.3°C. for buds). 

 Sudden thawing or several rapid alternations of freezing and thawing 

 did not seem injurious. 



It has been held that rapid thawing induces excessive transpiration 

 and prevents the return into the cell of the the sap withdrawn in freezing. 

 The trend of opinion among recent investigators, how^ever, fails to support 



