272 FUNDAMENTALS OF FRUIT PRODUCTION 



be more subject, though it seemingly appears in any situation. No 

 one side of the trees is uniformly injured, according to his observations, 

 though all cases occurring at any one time in a given orchard are likely 

 to be confined to some particular exposure. Trees which have made a 

 rather unusually large, or rather late, growth appear more liable to 

 injury. 



In the 1913 freeze, in the citrus regions of California, the crotches 

 were the parts of the trunk found most damaged. -"'' Crotch injury 

 and those forms of crown rot not due primarily to the attacks of parasitic 

 organisms are probably most frequently associated with early winter 

 injuries associated with immaturity. Consequent to the winter injury, 

 fungus infestation of the dead area may appear but, excepting the fire- 

 blight bacillus, no organism has been shown definitely to be the primary 

 causative agent in producing this disorder. 



Localized Injuries and Delayed Maturity. — Chandler^^ states: "The 

 wood at the base of the trunk and at the crotches of all rapidly^ growing 

 branches seems to reach a condition of maturity in early winter more 

 slowly than does other tissue. " 



This view corroborates studies by Mer^^^ on the duration of cambial 

 activity in various trees, reported in part as follows. "Just as it awakes 

 gradually in the different regions of a tree cambial activity ceases pro- 

 gressively at the end of summer. ... It disappears from the branches 

 before disappearing from the trunk. In trees that are closely grouped, it 

 leaves first the low branches, less vigorous than those of the top, and the 

 basal and median parts of these branches before their extremity. It is 

 only following this that it leaves the higher shoots. In the large branches 

 of an isolated tree it stops earlier at the tips than at the middle. It is at 

 the level of the basal swelling that it persists the longest. In the trunk 

 it stops first at the top, then at the middle and finally at the base. When 

 growth is not very active it ceases, on the contrary, earlier in the lower 

 region. ... It is in the portion of the trunk situated immediately 

 below the soil that cambial activity is confined last. 



"It is evident that in the regions of the trunk where the vegetative 

 activity is the most pronounced, because they are the youngest or 

 because they are the best nourished, that cambial activity awakes 

 first. . . . It is there also, that in general, it stops latest. On the other 

 hand, in all circumstances where growth is slow, we see cambial activity 

 manifesting itself slowly and stopping earlier. . . . Between the length 

 of the cambial activity and its intensity there is, then, a manifest 

 relation." 



This statement seems in itself adequate explanation for much of the 

 localization of winter injury associated with immaturity. Field studies 

 in several regions seem to correlate immaturity with this type of injury 

 rather uniformly. 



