March, 1922] JOHNSTON — UNDERCOOLING OF PEACH BUDS 
95 
Data showing the average temperature at which crystalHzation began and 
the average temperature immediately after crystal formation are designated 
in table i as UndercooHng" and "Freezing point" respectively. The 
Table i. Data Showing the Temperature of the Freezing Mixture, the Average Temperature 
at which Crystallization began {Undercooling) , and the Average Temperature Immediately 
after Crystal Formation {Freezing Point), together with the Ratio of Water Content to Dry 
Weight of Fruit Buds of the Elherta and Greensboro Peach. 
Date 
Temperature 
of 
Freezing 
Mixture 
Undercooling 
Freezing Point 
Elberta 
Gr'boro 
Elberta 
Gr'boro 
Deg. F. 
Deg. F. 
Deg. F. 
Deg. F. 
17.8 
18.5 
21.0 
20.5 
19.2 
19.6 
22.1 
21.6 
17.8 
17.6 
20.3 
19.6 
18. 1 
18.7 
21.6 
21,0 
18.5 
18.9 
21.6 
21.7 
19.0 
19.2 
22.8 
22.3 
19.4 
20.1 
24.4 
24.8 
22.3 
20.5 
24.6 
24.4 
Ratio of Water Content 
to Dry Weight 
Elberta 
ig2i 
Jan. 21 . . . 
Jan. 26. . . 
Feb. 12 . . , 
Feb. 18. . . 
Feb. 25 . . , 
Mar. 5. . . , 
Mar. II.. 
Mar. 14. . 
Deg. F. 
14.0 
15-8 
4-3 
7.5 
8.6 
6.4 
3-2 
2.8 
0.89 
0.82 
1.03 
0.94 
1.20 
1.05 
1. 21 
I.IO 
I.6I 
I-3I 
2.53 
2.01 
2.87 
2.57 
temperature of the cooling mixture was not exactly the same on any two 
days, thus making some measurements taken on different days not strictly 
comparable, but the data of the two varieties on any one day are com- 
parable. All the measurements were made in the laboratory shortly after 
the twigs had been cut from the trees. Twigs of similar size and similarly 
located on the trees were selected. The lower ends of these twigs when 
brought to the laboratory were cut off under water and placed in bottles 
of water in order to minimize the danger of drying out. Buds from the 
two varieties were alternately measured in pairs as a further precaution 
for securing comparable data between varieties. The time usually re- 
quired for a bud to undercool was about two minutes, although this varied 
somewhat with the temperature of the freezing mixture. These same 
data are represented graphically in figure i. 
In figure i the lower pair of graphs represents the undercooling and 
the upper pair the freezing point. From February 12 to March 14 each 
set of graphs shows a decided rise. This indicates that the sap in these 
buds as they continue to develop has a higher freezing point and that it 
can be undercooled to a less extent. The data of the first two observations 
are scarcely comparable with those of later dates because of the great dif- 
ference in temperature of the freezing mixtures, the rate of cooling being 
slower in the former cases than in the latter. There is very little difference 
between the freezing points of buds of these two varieties. Likewise there 
is but little difference in their undercoolings. Elberta, which is considered 
the less hardy variety, has in most cases a slightly lower undercooling point,, 
which is just the opposite of what might be expected. On March 14, how- 
ever, shortly before the petals opened, the extent of undercooling is 22.3° F. 
