360 FUNDAMENTALS OF FRUIT PRODUCTION 



or can be supercooled, at what temperature ice formation occurs or at 

 what temperature damage results. General sudden freezing following 

 supercooling is considered in itself injurious. ^^^ To what extent this 

 applies to fruit blossoms cannot be stated at present. Indeed it is possible 

 that under natural conditions supercooling as ordinarily understood 

 does not occur in fruit blossoms. The influence of capillarity on freezing 

 in these tissues cannot be stated now. It is, however, safe to conclude 

 that critical temperatures as determined by laboratory methods would 

 be somewhat lower than would appear from field observations with ordi- 

 nary thermometer exposures, because of the differences between air 

 temperatures and plant temperatures under the radiation conditions 

 accompanying most frosts. For the same reason precise determination 

 of killing points would not be of direct application in the orchard. Paren- 

 thetically it may be remarked that the insufficient recognition of radia- 

 tion effects on plant tissues in horticultural investigation may account 

 for many of the conflicting results secured. 



However, studies in artificial freezing are interesting, though the 

 high degree of humidity that accompanies them is not invariably present 

 in nature. This high humidity may serve conceivably to inoculate 

 the plants with freezing nuclei and cause freezing at higher temperature 

 than would be required in a drier atmosphere. Despite limitations, 

 however, the tests by artificial freezing possess considerable significance. 

 West and Edlefsen have reported some rather extended investigations 

 of this sort. 



In part, they summarize their results as follows: "Ben Davis apple buds in 

 full bloom have experienced temperatures of 25, 26, and 27°F. without injury, 

 but 28° usually killed about one-fifth. Twenty-nine degrees or above are safe 

 temperatures. Twenty-five degrees kills about one-half and 22° about nine- 

 tenths. On several occasions, however, apples matured on branches that experi- 

 enced 20° when the buds were in full bloom. 



"With Elberta peach buds in full bloom, 29°F. or above are the safe tem- 

 peratures, because even though occasionally 26, 27, and 28° do no damage, yet 

 on most occasions 28° will kill from one-fourth to one-half. Twenty-six degrees 

 kills about one-half of them and 22° about nine-tenths. Temperatures as low 

 as 18° have failed to kill all of them. 



"With sweet cherry buds in full bloom, 30°F. is the safe temperature; 25, 26, 

 27, 28° have done no damage, but 29° usually kills about one-fifth. Twenty- 

 five degrees usually kills about one-half, and when the buds were showing color 

 22° killed only two-fifths of the buds. 



"Sour cherries are hardier than the sweet varieties. When the buds were 

 showing color 23°F. did not harm them, and when they were in full bloom 26° 

 killed about one-fifth and 22° only two-fifths of them. 



"With apricots, 29°F. is the safe temperature; 26 and 27° killed about one- 

 fifth and 22° killed one-half. . . . 



"The foregoing figures refer to the buds when in full bloom. Starting from 



