Dec, 1922] HAWKINS EFFECT OF LOW TEMPERATURES 
555 
the different kinds of fruits and vegetables; altogether some fiteen or 
twenty thousand determinations have been made. In this work it was 
found that the freezing points of most of these fruits and vegetables lie 
between —.5° C. and — 2.5° C. The succulent plants, such as lettuce, 
cabbage, celery, and cauliflower, freeze at a considerably higher temperature 
than do potatoes, sweet potatoes, apples, and such produce, which have a 
relatively high dry weight. Some products, such as nuts, which have a 
very low water content, have a low freezing point. From our investigations 
in this field the conclusion seems obvious that all fleshy fruits and vegetables 
will be killed if exposed to a low enough temperature after ice crystals 
begin to form in the tissues. Many fruits and vegetables, however, can be 
cooled to temperatures below their freezing points and have the crystalliza- 
tion of the water actually take place within the tissues without apparent 
injury, and the occurrence of local injuries, that is, injuries to certain 
portions of the tissue, due to freezing, is quite common. An illustration of 
this point is found in the work of Jones, Miller, and Bailey^^ on potatoes. 
These writers show that a potato may be injured locally by freezing, the 
death of the cells being followed by browning of the cells around the fibro- 
vascular bundles or in the parenchyma itself. The major portion of the 
potato, however, might remain sound for a long time. Wright and Harvey^^ 
and Wright and Taylor^^ corroborated these results in their work on pota- 
toes. It is very doubtful, however, whether ice crystals are ever formed in 
the potato without injury to the tuber. In this respect they are different 
from some of the other vegetables and fruits. Apples may be frozen 
lightly and thawed without apparent injury. Hard, ripe Bartlett pears 
have been frozen solid, removed from the freezing room, and ripened 
normally without any indications that the tissues of the fruit had been 
injured by the solidification of the water. Ripe pears or immature pears 
of this variety may be seriously injured by freezing. With apples, slight 
freezing sometimes causes local discolorations around the fibrovascular 
bundles or dark-colored areas in the tissue. These problems are, of course, 
under investigation at the present time and are furnishing some interesting 
information. 
In freezing fruits and vegetables, they may frequently be undercooled 
far below the freezing point without the formation of ice or without any 
apparent injury to the tissues. It has been found that potatoes could 
sometimes be cooled as much as 10° C. below their freezing points, if allowed 
to remain undisturbed, before the inception of ice formation in the tissue. 
In certain instances they have been cooled as much as 6° C. below their 
Jones, L. R., Miller, M., and Bailey, E. Frost necrosis of potato tubers. Univ. 
Wis. Agr. Exp. Sta. Res. Bull. 46. 19 19. 
15 "Wright, R. C, and Harvey, R. B. Freezing point of potatoes as determined by the 
thermoelectric method. U. S. Dept. Agr. Bull. 895. 192 1. 
16 Wright, R. C, and Taylor, G. F. Freezing injury to potatoes when undercooled. 
U. S. Dept. Agr. Bull. 916. 1921. 
