256 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 



growers were prepared to believe that another of the unusual things 

 so usual in California had happened and that lemon trees had been 

 less injured than orange trees by the cold. In a few days, however, 

 the leaves of the lemon trees began to droop and turn brown; while 

 the orange leaves, where the temperature did not go too low, unrolled 

 and assumed their normal functions. Due to the slow physiological 

 changes in both fruit, foliage and wood following the freeze, it was 

 some time before accurate indications of the extent of damage became 

 visible. 



Effect on External Appearance of Fruit. The orange and lemon 

 fruits, while still frozen, often showed in the skin clear, icy areas 

 adjoining other areas which were not icy. A few days after the freeze 

 these fruits became spotted (figs. 3 and 4), caused by a shrinking of 

 the tissue between the oil-bearing cells and a consequent drawing 

 together of these more deeply-colored, oily portions of the skin. Soon 

 after the freeze lemons which were frozen very hard were covered 

 with white watery patches, which gave them a loathsome appearance. 

 A black mold frequently established itself on these fruits and they 

 shriveled and dried up on the trees. 



The degree to which fruit becomes spotted gives a good, early 

 indication of the severity with which it is damaged, especially with 

 oranges. If none of the oranges in a grove are spotted, the fruit may 

 have been injured, but usually there still will be fruit of value in the 

 grove. Where the freezing has been harder, spotted fruit will show 

 on the north side of the tree, and to some extent, there will be spotting 

 on the north side of fruit on the south side of the tree. The stem 

 end seems to be most easily spotted. In groves where north side 

 spotting is general, there is little fruit which will not show signs of 

 deterioration by the time three months have passed. The fruit which 

 is spotted is valueless, for though it may retain juice for some time, 

 it deteriorates so rapidly that it does not pay to ship it. Where the 

 fruit in all parts of the tree is spotted, but little value can be attached 

 to the crop. 



All citrus fruits are not subject in the same degree to this frost 

 spotting. The tangerine apparently is not subject to it and the 

 Valencia, while sometimes found badly marked, is much less suscep- 

 tible than either the navel or the Ruby Blood. Both the pomelo and 

 lemon are readily marked with these frost spots, the former fruit, 

 when exposed, being especially susceptible. The frost spots of both 

 the pomelo and lemon in time turn brown and become far more con- 

 spicuous on the yellow background of these fruits than the yellow 

 spots of the orange on the orange-colored background of that fruit. 



