556 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9. 
freezing points and then warmed to temperatures above the freezing point 
without any evidences of injury. The potatoes, of course, were maintained 
undisturbed during these experiments. 
A slight jar, such as would be caused by the slamming of the door of 
the freezing room, tapping the tubers gently with a lead pencil, or dropping 
them a short distance, promotes the inception of ice formation very readily 
in undercooled potatoes, and when once freezing begins, injury to the tissues 
is apparently sure to follow. Apples may be undercooled to a marked 
degree, and cranberries and cherries withstand temperatures considerably 
below their freezing points without freezing. Gooseberries have been stored 
for three months at a temperature of 4° C. below their freezing point and 
only II percent of the fruit were frozen. In general, fruits and vegetables 
with waxy epidermal coverings may be undercooled much farther than 
plants in which the cutinized or suberized layer is not so pronounced; for 
instance, lettuce, celery, and cauliflower are very easily inoculated and will 
not undercool much below their freezing points. Other factors besides 
these waxy coverings apparently also influence the degree of undercooling, 
as plugs of potatoes with the cut surfaces exposed will undercool as much as 
do whole tubers. It is quite possible that the concentration of the cell sap 
has considerable to do with these phenomena. Wright and Taylor have 
shown that the rate at which potatoes are cooled influences the degree 
below their freezing points to which they can be cooled without freezing. 
To put it briefly, a very rapid or a very slow fall in the temperature is not 
favorable to low undercooling. Other factors as yet unrecognized are 
undoubtedly concerned in these phenomena. 
A survey of the work on plant physiology, and especially on the phases 
relating to low-temperature storage and freezing, impresses one with the 
aptness of the statement frequently made, that ''plants are water with 
some other things in it." This is especially applicable to fruits and vege- 
tables which are commonly placed in cold storage. The water content of 
this type of produce varies from about 95 to 65 percent. The chemical 
processes in the plant are in a watery solution, and, as far as they have been 
investigated, follow much the same course as they do outside the plant. 
In freezing, the apple or potato behaves in about the same way as does a 
solution as regards undercooling, inoculation, and the crystallizing out of 
the water. We have, of course, in this aqueous solution a great many 
interrelated reactions going on at the same time, and knowledge of each 
process and of its relation to the other processes is necessary for a good 
understanding of the subject. 
Bureau of Plant Industry, 
U. S. Department of Agriculture 
