PRUNING—THE SEASON 449 



results in a shading of leaves lower in the tree and possibly in reduced 

 rates of photosynthesis and of food manufacture. However, a light 

 heading back or pinching of the terminals of the grape early in the season, 

 thus temporarily checking new shoot growth, is said to aid materially 

 the setting of fruit in certain varieties.^ This is a concentration effect, 

 though the practice is of special rather than general application. On the 

 other hand thinning out has no such tendency to encourage the develop- 

 ment of secondary; shoots certainly they are not formed to anything 

 like the same extent as with summer heading. More light is admitted to 

 the interior of the plant which is better supplied with nutrients and 

 moisture and the result is an increased accumulation of elaborated foods. 

 The results attending a well distributed thinning of the shoots and smaller 

 branches would be more pronounced in this direction than those following 

 a coarse or bulk thinning. 



When soil conditions, particularly^ moisture and nutrient supply, 

 encourage new vegetative growth, summer pnming is much less likely to 

 exert concentrating effects than it is when less moisture and less nitrogen 

 are available. Indeed its influence may be the reverse, particularly if the 

 summer pruning has been mainly heading back. Generally speaking, it is 

 easier to secure the concentration effects of summer pruning when the 

 available soil moisture and nitrates are not too high and when atmospheric 

 conditions favor a high transpiration rate. These, it will be recognized, 

 are the conditions under which it has been suggested by Chandler'" that 

 summer pruning can be employed advantageously as a moisture- 

 conserving measure to prevent the wilting of partly grown fruits on 

 heavily laden and vigorously growing trees. The influence of certain 

 summer pruning practices on the formation of fruit buds, discussed a 

 little later, is probably due to their concentrating effect. 



In a general way it may be stated that summer pruning is often 

 very useful because of its influence in diverting the energies of the plant 

 into other channels. In the average plant most of the watersprouts and 

 suckers (except those used for renewal purposes) are worse than useless. 

 They dissipate- energies and yield little in return. Their prompt 

 removal is a conservation measure and is particularly important in 

 certain fruits like the grape and in nearly all young trees. The longer 

 the delay in cutting them out the less is gained by removing them. 

 Practically the same statement holds for the early summer removal of a 

 portion of the barren shoots in the grape and certain other plants. 

 Midsummer or late summer pruning may be desirable occasionally, in 

 so far as it reduces transpiration losses and indirectly aids in the sizing 

 and coloration of the fruit. 



It should be reiterated that the concentrating effect of pruning does 

 not necessarily invigorate the plant as a whole. In fact it may have 

 exactly the opposite influence, though certain parts are favored by the 



