8 BULLETIjST 1099, V. 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 

 freeze 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 fi^eezing 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 j^oung fruits first and on the top side, 

 on which dew had deposited. 



Xo differences could be detected in the freezing points of the 

 plants in 26 varieties in this field. If differences exist it 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 fi-eezing point of tomato leaves was found to 

 be 30.22° while stems froze at 29.99° F. 



Tomatoes which lie directly upon the ground are warmed by 

 conduction from the warm eaith 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 

 vStates 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. 



