342 CITRUS FRUITS AND THEIR CULTURE. 



it is killed to the ground, and may frequently be split open 

 if the cold is sufficiently intense. As with the branches, 

 its resistant power is in direct ratio to the diameter. It 

 does not appear that there should be much difference in 

 ability to withstand cold, between a citrus trunk four 

 inches in diameter and one eight inches in diameter, but 

 such is the case, nevertheless. It may be that larger trees 

 become more dormant than smaller ones and their sap does 

 not respond so readily to elevations of temperature. 



The weakest spot, in the whole anatomy of a budded 

 or grafted citrus tree, is the point of union of stock and 

 cion. This point should be protected by placing about 

 it a mound of earth and, moreover, the union should be as 

 close to the ground as possible. Protection afforded the 

 trunk by a dense mass of foliage, twigs and branches is 

 frequently not appreciated to its fullest extent. The warm 

 air is held to some extent, and the cold is prevented from 

 penetrating to the framework of the tree. Low-headed 

 trees are preferable to high-headed ones, because in the 

 former case, the branches serve as a protection to the 

 trunk. High-headed trees should not be grown in exposed 

 regions. 



On the Fruit. Up to the present time no statement 

 has been made as to whether the fruit of any variety of 

 citrus is more resistant to cold than others. It is prob- 

 able that no appreciable difference exists, or if there is a 

 difference, it is too slight to be of any practical value. 



Small, whitish specks, 1-2 millimeter in diameter, 

 appear in the tissues of the fruit after it has been slightly 

 touched by frost. These are evidently due to chemical 

 changes and are probably present in all kinds of citrus 

 fruits. They have been noted in lemons, sweet oranges, 

 mandarin oranges, kumquats and pomelos. Their pres- 



