442 FUNDAMENTALS OF FRUIT PRODUCTION 



growth — 58 per cent, in the Wagener trees, 44 per cent, in Yellow Newtown, 

 44 per cent, in Jonathan and 47 per cent, in Grimes — than those that 

 were pruned during the dormant season only. A part of this increased 

 growth came before the time of summer pruning (about July 1), but the 

 larger part of it was produced during the summer months following the 

 pruning. The growth produced before the time of summer pruning is to 

 be regarded as the consequence of a summer pruning treatment of the same 

 kind the preceding season; the growth after the pruning was a direct 

 response to that pruning. There was practically no difference between 

 the summer and winter pruned trees in their net increase in size, except 

 in Jonathan. The winter pruned trees of that variety showed a greater 

 net growth, principally on account of the great amount of wood removed by 

 the summer treatment. Vincenf*^ in Idaho has reported the 11-year 

 record of an apple orchard of Jonathan, Rome, Grimes and Wagener a 

 part of which received only winter pruning from the start while the other 

 part received only summer pruning (Aug. 6 to Sept. 6). In kind and 

 amount the pruning of the two portions was as nearly as possible. Table 

 15 summarizes some of the growth records of these trees. For the most 

 part the average heights, widths and trunk circumferences were slightly 

 greater in the winter pruned than in the summer pruned trees, while the 

 reverse was true in regard to average shoot lengths. In no case, how- 

 ever, were the differences large enough to be significant. Clearly, 

 summer pruning exerted no dwarfing influence in this orchard. 



These almost diametrically opposite results attending summer pruning 

 in carefully controlled experimental work can be harmonized. The 

 tree is to be regarded as a system in mobile equilibrium. This equili- 

 brium involves a condition of balance between part and part and between 

 constituent and constituent within the plant and a condition of adjust- 

 ment to the environment without. Chief among these factors of environ- 

 ment are temperature, light, moisture and food supply. Growth of any 

 kind is a response to the condition of the equilibrium within and of 

 the adjustment without. Pruning, at any time — and more especially 

 summer pruning — disturbs both the adjustment to the environment 

 without and the balance within. The immediate effect on the tree as a 

 whole of any summer pruning is to reduce the carbohydrate supply 

 and the rate of carbohydrate manufacture and at the same time to 

 increase the supply of water and other nutrients, particularly nitrates, 

 that is available to the rest of the plant. The size or amount of this 

 influence depends on: (1) the severity, (2) the kind and (3) the time of 

 the pruning and on (4) the moisture and (5) the nutrient supply available 

 in the soil. Its general effect on growth therefore may be expected to 

 correspond closely to that of fertilization and irrigation at that particular 

 time. If the pruning is not severe enough to reduce carbohydrate sup- 

 ply and carbohydrate manufacture to the point where they limit new 



