PRUNING— THE METHOD 425 



of the heavily pruned Rome trees, the proportion of such lateral fruit buds was 

 8 to 1 under the two pruning treatments. Furthermore, the distribution of these 

 lateral fruit buds is such that a given heading-back (for instance, 50 per cent) 

 would remove a much larger percentage than an equall}^ severe thinning out. 

 This percentage, in the case of Esopus, would be enough greater more than to 

 counterbalance the effect upon total fruit production of larger numbers of such 

 lateral fruit buds. 



"Taking all these facts into consideration, it is evident that the effect of 

 thinning-out and likewise of heading back upon fruit-bud formation varies 

 greatly with the variety. The pruning practice that will lead to the largest 

 fruit-bud production in one variety will not necessarily lead to it in another. 

 Thus it becomes important for the grower to become- better acquainted with 

 the exact fruiting habits of his varieties under his conditions as well as to the 

 response that these varieties make to various pruning practices." 



Thinning and Heading Lead to Different Nutritive Conditions. — The 

 explanation of the varying effects of thinning out and of heading back 

 on fruit-bud formation is not found exclusviely in the different fruiting 

 habits of the several species and varieties. New growth is made chiefly 

 at the expense of stored foods, particularly carbohydrates. In the section 

 on Nutrition data are presented showing that the younger wood is 

 comparatively richer in food reserves than older tissues. Heading back, 

 therefore, removes a larger amount of the tree reserves than a correspond- 

 ingly severe thinning out and leaves it less able to recuperate, especially 

 if the pruning has been severe. 



It is also pointed out in the section on Nutrition that the initiation 

 of the fruitful condition, or in other words fruit-bud formation, is associ- 

 ated with an accumulation of carbohydrates in the regions where fruit 

 buds can be formed. Carbohydrate accumulation in turn depends on 

 carbohydrate manufacture on the one hand and on carbohydrate utiliza- 

 tion on the other. When the latter process lags behind the former, oppor- 

 tunity is finally afforded for the laying-down of fruit buds. In the last 

 analysis, therefore, pruning influences fruit -bud formation to the extent 

 that it influences carbohydrate accumulation or carbohydrate utilization 

 or the status of the ever changing ratio between them. 



Thinning out not only removes less stored food than a corresponding 

 heading back, but, as just pointed out, it also leads to increased fruit- 

 spur formation and decreased shoot growth. This means decreased 

 carbohydrate utilization and increased carbohydrate manufacture, 

 because spurs are short growths with relatively large leaf surfaces. Their 

 growth is made very early in the season and from then on they are manu- 

 facturing and accumulating rather than spending or dissipating organs. 

 On the other hand heading back produces fewer of these short growths 

 and more of the longer and stronger shoots that complete their growth 

 much later. Consequently they more nearly exhaust the plant's re- 



