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 haA^e 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 (S) . 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 clue 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 precede 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 leaves and fruits. A thickened cuticle is of impor- 

 111004—22^ 2 



