8 BULLETIN 1099, U. S. DEPARTMENT OF AGRICULTURE. 
lag, to have a short duration of temperatures somewhat below freez- 
ing without injuring the fruits. During the night considerable dew 
was deposited in droplets on the upper surface of the tomatoes. The 
dew began to freeze when the temperature inside of the tomatoes 
reached 31.1° F. This is scarcely less undercooling than the water 
on adjacent leaves showed, but dew on the leaves froze a little 
quicker than that on the fruits because of the radiation of heat from 
the latter. When the tomatoes had reached 30.6° F., they began to 
treeze at the surface where the thermometers had been introduced, 
and dark-colored areas became visible, due to changes in the reflec- 
tion of light from the frozen tissue. The final freezing points of 
fruits Nos. 1, 2, and 3 were 30.6°, 30.4°, and 30.2° F., respectively. 
Owing to the heat liberated by the freezing out of water, the inside 
temperature of the tomatoes did not fall below 30° at any time, al- 
though the outside temperature fell to 26.9° F. In tomatoes which 
were undisturbed it was observed that freezing did not begin as soon 
in sound tomatoes as in those in which the skin was broken. It will 
be noted that no undercooling was recorded. This was probably due 
to the freezing dew on the surface of the tomatoes. Previous in- 
vestigations by the Bureau of Plant Industry of freezing injuries 
to potatoes showed that wet potatoes freeze more readily than dry 
ones (6). Freezing began on young fruits first and on the top side. 
on which dew had deposited. . 
No differences could be detected in the freezing points of the 
plants in 26 varieties in this field. If differences exist 1t would re- 
quire carefully equalized temperatures to detect them. The young 
leaves freeze first, and in these the injury occurs first along the 
vines. The average freezing point of tomato leaves was found to 
be 30.22° while stems froze at 29.99° F. 
Tomatoes which le directly upon the ground are warmed by 
conduction from the warm earth and do not freeze as quickly as those 
situated up on the vine. When the vines are very leafy those tomatoes 
which hang on the inner branches are not frozen as soon as exposed 
fruits, because they are protected from radiating their heat by the 
surrounding leaves. 
SUMMARY. 
(1) A large portion of the tomato crop grown in the Southern 
States and shipped north in the late winter is in constant danger of 
frost injury while in transit. 
(2) The average freezing point of 19 commercial varieties was 
determined to be 30.46° F. 
(3) A difference of 0.89° F. was found between the freezing points 
of certain varieties of tomatoes. 
