340 CITRUS FRUITS AND THEIR CULTURE. 



defoliated by cold, the danger of injury to the branches 

 and twigs is very materially increased. 



As an approximation, it may be said that green fruit 

 is injured at 29 degrees, and ripe fruit at 26 degrees. Dor- 

 mant sweet oranges have been known to stand a tempera- 

 ture of 18 to 20 degrees F., for a short period. This ap- 

 proaches the limit. A large Satsuma tree on the Experi- 

 ment Station grounds at Lake City, Fla., stood, on one oc- 

 casion, a temperature of 16.5 degrees F. without loss of 

 foliage. The tree was dormant at the time. On the other 

 hand, when the sap is moving in the trees they may be 

 severely injured or killed to the ground even at much 

 higher temperatures. One of the most critical periods 

 is when the trees are in bloom. 



EFFECTS OF COLD. 



On the Leaves. The effect of a slight amount of cold 

 on the tree is to curl the leaves to such an extent as to 

 make them appear as though suffering from lack of mois- 

 ture. If chilled only to a slight extent, they may regain 

 their normal condition and still remain on the tree. 

 Whether leaves thus affected will serve a useful purpose, 

 on the tree, as long as those which have not been so affect- 

 ed, is doubtful. At any rate it appears that their useful- 

 ness is materially impaired for one season at least and it 

 is possible that the life of such leaves is shortened. 



If still further frosted, the leaves are curled and, in the 

 course of a few days, drop from the trees. Usually the 

 upper leaves fall before the lower, some of the latter fre- 

 quently remaining, even when the upper portion of the tree 

 is practically defoliated, as shown in Fig. 76. Defoliated 



