450 FUNDAMENTALS OF FRUIT PRODUCTION 



process. Thus a heavily laden peach tree pruned in late July as a protec- 

 tion against drought is probably weakened by the operation and may 

 show the effects in the new growth put out the following spring, though 

 the pruning operation enabled the fruit to mature properly. The 

 situation is simply another aspect of a problem constantly encountered 

 in pruning practice — that of subordinating or even eliminating one part 

 in the interest of another. 



Influence on New Spur Formation. — The influence of summer pruning 

 on new shoot formation and consequently on the fruit-producing wood 

 in plants bearing on shoots or canes has been discussed. There 

 remains consideration of its influence on new spur formation. Spurs are 

 generally formed from lateral buds on the long growths of the current 

 or of the preceding season. Only a certain percentage of these grow out 

 into spurs, the number depending on many factors, among the more 

 important of which are (1) the supply of nutrients and elaborated food 

 materials available for their growth and (2) the relative stage of develop- 

 ment or the size of the buds themselves. The influence of summer 

 pruning on the supply of available foods has just been considered under 

 the head of Concentration; consequently that aspect of the question 

 need not be discussed further. 



Observation shows that in almost all species there are considerable 

 differences in the size of the lateral buds on the long growths or shoots. 

 Usually those on the basal portion are small and inclined to remain 

 dormant unless stimulated into growth by some special pruning or 

 other treatment; the buds on the median and terminal portions of the 

 shoot are better developed and grow out readily, to form either shoots or 

 spurs. Apparently their greater size and development is due largely to 

 the better light supply and to the more favorable location for food manu- 

 facture, of the leaves that subtended them. Obviously almost any 

 pruning and particularly any summer pruning will influence the amount 

 of light reaching the leaves on the remaining shoots. In many fruits sum- 

 mer heading back, unless very light and done comparatively late in 

 the season, encourages the formation of laterals or secondary shoots and 

 consequently produces poorer conditions for photosynthesis in the lower 

 parts of the plant. At the same time, as shown later under Pinching, 

 it results in thickening the bark on the lower portion of the shoot and 

 therefore in different food storage conditions that are associated with the 

 change in the relative proportions of the several tissues. These effects 

 may outweigh in importance those occasioned by greater shading. There 

 is reason to believe that in at least some fruits summer heading acts as a 

 stimulus to fruit-bud formation on the current season's shoots. On the 

 other hand thinning out admits more light to the leaves on the lower 

 part of the shoots and thus encourages the elaboration of foods and the 

 formation of larger and stronger buds. Summer thinning therefore 



