PRUNING PRINCIPLES 103 



The data obtained show that except at the very first, neither in 

 total length of growth nor in increase of trunk diameter, have the 

 heavily pruned trees made as satisfactory a gain as the lightly 

 pruned ones. The only possible deduction from the figures is that 

 continued heavy pruning acts as an inhiliitor of growth rather than 

 as a stimulant. In must be borne in mind, however, that no account 

 was taken of the fact that the average diameter of the yearly 

 growth of the heavily pruned block was greater than of the lightly 

 pruned block, so that the real difference in amount or weight of 

 actual tissue produced was not as much as indicated in the table. 

 It is significant to note in this connection that in all the orchards 

 the lightly pruned trees are noticeably larger than the heavily 

 pruned ones. With few exceptions the increase of diameter of 

 trunk has been in inverse ratio to the amount of wood cut off. 



Thus far we find that heavy pruning forces a rank growth, al- 

 though it retards, as a whole, the production of wood tissue. There 

 is presented an interesting question of whether heavy pruning and 

 particularly heavy heading back, tends to make more stocky that 

 portion of a branch produced one or more years previous to the 

 pruning. In other words, can a long slender branch be made more 

 stocky by vigorous heading in at the extremity? 



96. Effect of heading-back on stockiness. — On the young trees on 

 which measurements were made to test this point the results were 

 not as clear cut as could be wished, yet they indicate on the whole, 

 that heavy heading-in tends to thicken the branch more rapidly 

 than does light pruning [and this may be traced] e^'en as far down 

 as that segment of branch produced four years previously. This 

 is not well correlated to our own results regarding the increase in 

 trunk diameter as related to pruning. We frankly admit a high 

 probable error in this part of our data and do not lay undue em- 

 phasis upon this phase. It must be substantiated by further work. 



In the matter of frultfulness. Interesting correlations were se- 

 cured. In the one middle-aged orchard in the test, heavy pruning 

 proved to be a stimulant to fruit production, whereas in the younger 

 orchards, it acted as an inhibitor. 



In another six-year-old orchard the only fruits produced were 

 upon the lightly pruned block, and in a five-year-old orchard the 

 lightly pruned block averaged 85 per cent, and the heavily pruned 

 block 50 per cent. In young trees heavy pruning delayed fruit bear- 

 ing and light pruning encouraged it, but in older trees that bad been 

 bearing for some time and were in only fair vigor at the beginning 

 of the experiment, the vigorous pruning stimulated fruit production. 

 Heavy pruning also produced strong new shoots, but did not in- 

 duce "as great a total amount of new growth as light pruning, nor 

 did it produce as great an Increase in diameter of trunk or size 

 of tree. 



97. Season of pruning vs. vigor and fruitfulness. — We will now 

 pass on the influence of pruning at various seasons on the vigor 

 and fruitfulness of the trees. In every case either heavy or mod- 



