AMERICAN 
JOURNAL OF BOTANY 
Vol. IX March, 1922 No. 3 
UNDERCOOLING OF PEACH BUDS 
Earl S. Johnston 
(Received for publication June 8, 192 1) 
One method of determining hardiness of fruit buds is that of estimating 
the percentage of injury after the buds have been subjected to low tem- 
peratures under natural or artificial conditions. West and Edlefsen^ give a 
table compiled from the results of other workers showing the danger points 
for various kinds of fruit at three different developmental stages. The 
danger point for peaches at the time the petals are closed, but are just 
showing color, varies from 20° to 29° F. Their own very extensive studies 
show that Elberta peach buds in full bloom are safe at 29° F. and above. 
They state that occasionally temperatures of 26°, 27°, and 28° F. do no 
damage, but that usually one of 28° F. kills from one fourth to one half the 
buds, and a temperature of 22° F. kills nine tenths, while one of 18° F. fails 
to kill all of them. The method of estimating the injury is not very satis- 
factory in cases where the degree of hardiness is to be determined. It is 
very desirable that some convenient physical measurement of hardiness of 
fruit buds be worked out in order to ascertain more definitely the relation 
between the resistance offered by such buds to low temperature and various 
environmental conditions such as moisture, temperature, fertilizers, etc. 
Johnston^ suggested that the ratio of water content to dry weight of fruit 
buds might serve as a possible index, but sufficient work has not yet been 
done to warrant its general use. Experimental results of various investi- 
gators have not always been in agreement regarding the value of the freezing- 
point depression of expressed saps as an indication of hardiness. Further- 
more, there are a number of important conditions necessarily neglected in 
measuring the undercooling of expressed saps. For example, it has been 
shown by Bigelow and Rykenboer^ 
That decidedly greater supercooling can be produced in capillary tubes than in tubes 
of larger diameter. 
^ West, F. L., and Edlefsen, N. E. Freezing of peach buds. Jour. Agr. Res. 20: 655- 
662. 1921. 
2 Johnston, E. S. An index of hardiness in peach buds. Amer. Jour. Bot. 6: 373- 
379- 1919- 
^ Bigelow, S. L., and Rykenboer, E. A. Capillary phenomena and supercooling- 
Jour. Phys. Chem. 21: 474-512. 1917. 
The Journal for February (9: 47-92) was issued March 20, 1922. 
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