448 FUNDAMENTALS OF FRUIT PRODUCTION 



always reached, unless the operation is performed shortly before the begin- 

 ning of the dormant season, when an increase in the severity of the pruning 

 results in forcing into growth buds that otherwise would remain dormant 

 until the following spring. At this point its general effect changes from 

 conservation to dissipation since the new tissues demand not only soil 

 nutrients and moisture but elaborated foods as well. The branches, 

 canes or shoots remaining and perhaps the whole plant, are left weaker 

 in that they are likely to enter the dormant season less richly supplied 

 with elaborated food materials. In general the conservation effects of 

 any pruning cease when it promotes greater utilization of reserve foods 

 in the building of new tissue. Were these effects (that is, the ratio that 

 they bear to the total effects) of summer pruning plotted in a curve as 

 they vary with the severity of the pruning this curve would start close to 

 the 100 per cent value with very light pruning and fall steadily with each 

 increase in severity until the zero point is reached. Furthermore this 

 general situation would obtain regardless of the kind of the pruning or of 

 the exact time of the operation, though in no two cases could the curves 

 be expected to be exactly parallel. 



Closely related to the stimulating effect of varying amounts of summer 

 pruning is the influence of the stage of seasonal development at which it 

 is done. In general a very early summer pruning, particularly if it 

 consists in thinning out, is most effective in diverting the energies of 

 the plant into other developing or already developed tissues. It may 

 lead to greater elongation of shoots, to shorter internodes and more 

 leaves, possibly to the formation of side branches or to several other 

 growth responses or it may simply result in a more efficient functioning 

 of the remaining tissues. This, for instance, is the general effect of the 

 prompt removal of watersprouts, suckers or other shoots just as they are 

 starting. If the pruning is done a little later, during the period of most 

 rapid vegetative growth, it may have a concentrating effect (that is, 

 lead to the greater accumulation of elaborated foods) or it may have the 

 opposite effect and force out a crop of secondary shoots, the kind of the 

 response varying with the severity and kind of the pruning. Pruning 

 late in the growing season, if not too severe, is almost sure to have a 

 concentrating effect (for the particular parts affected), since no new 

 growth will take place to utilize the stored foods and there will be still 

 further accumulations resulting from the increased supply of nutrients 

 and of light. 



Of the two kinds of summer pruning, thinning out generally has a 

 much greater concentrating effect than heading back. The latter 

 practice, unless it consists in a mere pinching out of the terminals or 

 unless it comes very late in the season, results immediately in the forma- 

 tion of numerous secondary lateral branches. Their development 

 consumes food materials that have been, or are being, manufactured and 



