EFFECTS OF FREEZES ON CITRUS IN CALIFORNIA 261 



bark on limbs had been split, and the fruit on these limbs had not been 

 noticeably injured. 



The loosening of the bark in most cases signified the killing of the 

 cambium layer, but this was not always the case, because several 

 months after the freeze, it was common to find bark, which had 

 loosened along one edge but which had continued to live and grow, 

 forming a new layer of wood (fig. 11). One tree was found where a 

 strip of bark had completely separated from the tree, forming a bridge. 

 The bark was alive and had developed a layer of wood and a new 

 bark had formed next to the tree. 



The most surprising feature in connection with the severe bark 

 splitting on the trunks has been, in many cases, the comparatively 

 slight injury to the tops and foliage. Often there was bark splitting 

 when there was but little frost damage to either fruit or foliage. 



Some lemon groves of large old trees were observed that showed 

 much cracking and checking on the limbs and trunks, where similar, 

 adjoining groves, apparently as severely injured, showed almost no 

 checking. 



While it is true that in most cases where the bark was split and 

 loosened from the tree it was killed, it does not follow that when 

 the bark was killed it always loosened. Instances were common where 

 trees were girdled with frozen bark and the bark remained perfectly 

 tight. Sometimes these girdled trees showed no foliage damage and 

 there would be no suspicion that they had been injured until sud- 

 denly, perhaps four months after the freeze, the leaves would droop 

 and the tree would die. 



In Florida the area of bark immediately around the bud-union 

 is very susceptible to injury by freezing, being more tender than 

 the bark on other portions of the trunk. This greater tenderness of 

 the bud-union was not noticeable in California, the bark on the other 

 portions of the trunk being injured just as readily as around the 

 bud-union. In California the point most susceptible to injury seems 

 to be in the crotches of the limbs. 



BELATIVE HARDINESS OF DIFFEEENT VARIETIES AND SPECIES OF 



CITRUS FRUITS 



Relative Hardiness of Trees. The freeze brought out marked 

 differences in the hardiness of the several varieties of citrus trees 

 grown in California. It also demonstrated that the relative hardiness 

 of the trees of a variety is not the same as the relative hardiness of 

 the fruits of that variety, and this fact must be borne in mind in order 

 to avoid confusion. 



