288 FUNDAMENTALS OF FRUIT PRODUCTION 



the more tender variety of the two studied shows this change in greater 

 degree. 



Contributing Factors. — Roberts, ^"^^ in Wisconsin, investigating blos- 

 som bud kilHng in the sour cherry, concluded that suceptibility is in direct 

 relation to the degree of advancement, the more advanced blossoms 

 suffering most. He states: "The amount of injury is in relation to 

 the degree of development of the blossom buds, which, in turn, is usually 

 in [inverse] proportion to the amount of growth the tree is making." 

 These conclusions were reached after microscopic investigation as well 

 as field studies. 



The position of the hardiest buds was investigated by Chandler^^ 

 whose report follows, in part: . . . "the hardy buds are those borne at 

 the base of the whips (last year's growth). ... at the base of the 

 whips on trees not cut back only a slightly larger percentage of buds were 

 killed than were killed at the tips of cut back trees. . . . Now it is 

 possible to head back so severely that no fruit buds will be formed except 

 at the outer end of the branches. This is especially true if the tree has 

 a narrow dense head. ... If the tree be spreading in form, heading 

 back is not so likely to cause the next season's wood to be in very long 

 whips that either have branches at the basal nodes instead of fruit buds, 

 or have the leaves at these basal nodes killed by the shade before fruit 

 buds can be formed. This is true because the spreading heads would 

 afford room for a larger number of whips to grow and obtain light, and 

 the larger the number of nearly equal growing whips, other conditions 

 of the tree being equal, the shorter necessarily will be the growth in 

 each whip." Data are cited showing a loss of 60.2 per cent, of fruit 

 buds on a large low-growing, spreading Oldmixon as compared with 

 86.4 per cent, on a tree of the same variety making very large, upright 

 growth and 90.8 per cent, on still another Oldmixon making small 

 upright growth. 



Protective Measures. — Late entrance into the resting stage has been 

 said above to cause a delay in breaking the rest period. This may be 

 effected in a number of ways. 



Pruning. — One of the means of inducing late growth and late entrance 

 into the resting period is pruning heavily enough to stimulate vigorous 

 growth. Chandler^^ reports results of investigations in forcing twigs 

 of a large number of peach varieties which he summarizes as follows: 



"Average per cent, started on trees making large growth 



(cut back) 20.5 



Average per cent, started on trees making small growth 



(not cut back) 31.2 



Number of varieties in which trees not cut back started first . . 20 



Number of varieties in which trees cut back started first 3. 



Number in which both started about equally 4. 



