PRUNING— THE SEASON 451 



tends to encourage fruit-spur formation. This is in a sense another 

 concentrating effect of summer pruning. It is evident from what has 

 been said that the earlier in the season the pruning is done the greater is 

 its influence in this direction. 



Gardner 21 has reported that in young apple trees not yet in bearing 

 greatly increased fruit-spur formation follows early summer pruning 

 in addition to winter pruning. This is not so much because of the better 

 spur production from the buds left on the primary shoots after the 

 summer pruning as because after the pruning many secondary shoots are 

 produced on which the buds grow out readily to form new spurs the 

 following season. In apples nearly all the buds on these late summer 

 secondary shoots enter the winter in practically the same condition as, and 

 are comparable in every way to, the buds on the median and terminal por- 

 tions of the primary shoots. ^^ j^ f^g^ ^^e of the most useful purposes 

 served by the early summer pruning of young vigorously growing spur 

 bearing trees Hke the apple is to increase the number of spurs over that 

 secured by winter pruning alone. It is worthy of mention that spurs 

 developing from these secondary late summer shoots are as a rule 

 especially strong, vigorous and likely to produce fruit buds. 



Influence on Fruit-hud Formation. — In the section on Nutrition 

 it is shown that, in all cases studied, fruit-bud differentiation is associated 

 with carbohydrate accumulation in the immediate vicinity of the buds 

 concerned. The work of Magness^^ on young apple trees indicates that 

 this accumulation takes place principally where there is the greatest 

 effective leaf area. In other words, within certain limits those spurs 

 that have the largest and best lighted leaves accumulate the largest 

 reserves of carbohydrates and differentiate the most fruit buds. He 

 found that by partial or complete defoliation of spurs well supplied with 

 leaves, fruit-bud formation on these spurs could be entirely prevented, 

 even though adjacent spurs retaining their full complements of leaves 

 formed fruit buds freely. Similarly he found that the formation of 

 lateral fruit buds took place only in the axils of good sized, well lighted 

 leaves. 



Magness^^ summarizes his results as follows: "Fruit-bud initiation will not 

 take place, and fruit buds will not form in most varieties in the absence of a fair 

 amount of leaf area in the tree. 



"Food material stored in the tree through the dormant season is apparently 

 stored largely in the tissue adjacent to the leaves in which it was manufactured. 

 This is shown by the fact that the defoliated portion does not develop as strongly 

 and well during the spring following the treatment, as does the undefoliated 

 portion. 



"Leaf area in one part of the tree will usually not supply food material to 

 the buds in another part to the extent necessary to cause them to become fruit 

 buds. DefoHating one-half of a tree has Uttle influence upon the undefoliated 



