FROST INJURY TO TOMATOES. 5 
always occurred first in the tissue directly beneath each drop of 
water, and there was no doubt that inoculation of this tissue from 
contact with ice at these points caused the tissue to freeze. Earliana 
and Sunnybrook tomatoes showed frozen spots more quickly than 
the Beauty variety, and the latter froze much quicker than the 
Trucker’s Favorite, Ponderosa, Greater Baltimore, and Stone varie- 
ties. Green tomatoes always undercooled less than ripe tomatoes of 
the same variety, but the difference between the undercooling points 
of ripe and green tomatoes in the Earliana type is less than in other 
varieties. 
Some tomato varieties have a marked tendency to crack at the stem 
end. This is especially true of Chalk’s Early Jewel, Earliana, New 
Century, and Sunnybrook Earliana. Such tomatoes undergo scarcely 
any undercooling and are therefore easily injured. But even when 
the skin is not visibly broken the Earliana variety does not under- 
cool so much as some other varieties, as, for example, the New Cen- 
tury, which resembles Trucker’s Favorite and Livingston’s Globe 
in that it has a tough cuticle (3). Hundreds of tomatoes of several 
varieties were tested, but none were found with freezing points 
below 29.78° F. A tough skin and no tendency to crack at the stem 
end are evidently good characters to breed for in order to obtain 
varieties resistant to freezing. 
In those varieties in which the blossom end turns red much before 
the stem end freezing occurs first at the stem end. The freezing 
points of the two ends of the tomato were determined by thermo- 
couples. In partly ripened tomatoes tissue from the ripe blossom 
end showed a freezing-point depression a few tenths of a degree 
lower than tissue from the green stem end; however, in no case did 
it amount to as much as 0.4° F. This difference may be due to the 
formation of sugars in the ripening cells. 
EFFECT OF COLD ON THE TOMATO PLANT. 
The tomato plant belongs to a class of annuals which show but 
little adaptation to low temperature and can not be frozen without 
killing. On exposure to low temperature the plants become somewhat 
more difficult to freeze—that is, the freezing point is lowered—but as 
soon as ice formation occurs within the tissues the cells are killed. 
During the usual weather conditions which pr ecede the first killing 
frost in autumn the night temperature is usually somewhat above 
32° F. but low enough to increase the accumulation of osmotically 
active sugars, with a consequent lowering of the freezing point of the 
plant sap. Attendant also upon the low temperature there may be a 
stopping of growth, with the formation of a thicker cuticle over the 
surface of young esas and fruits. A thickened cuticle is of impor- 
111004—22 
