238 EXPEEIMENT STATION EECORD. [Vol.36 



pruned during the dormant season and also given a heavy early summer (July 

 1 to 10) thinning out and heading back. Records of growth under the varying 

 pruning treatments included number and length of shoots, shoot diameter, 

 trunk circumference, and number and distribution of fruit spurs. 



The results of this investigation as a whole are summarized as follows : 



" The data relating to shoot growth indicate that on the average the unpruned 

 tree increases in size a little more rapidly than the tree that is winter pruned 

 only, or that is both winter and summer pruned. Its average annual shoot 

 growth is less, but it loses none of this by pruning, and hence its net increase 

 is greater. Broadly speaking, there is but little difference in increase in size 

 between trees that are winter pruned only and those that are both winter and 

 summer pruned. The summer-pruned trees lose more shoot growth from prun- 

 ing, but they produce nearly enough more to compensate for the additional 

 loss. 



" The amount of shoot growth produced any one season by young apple trees 

 that have not yet developed many spurs is closely correlated with the amount 

 they made the preceding season and shows little correlation with the amount 

 of (i. e., the severity of) their winter pruning. Likewise the amount of shoot 

 growth produced late in the summer, following early summer pruning, is closely 

 correlated with the amount of the shoot growth possessed by the tree at the 

 time of summer pruning and shows little correlation with the amount of (i. e.. 

 the severity of) the summer pruning. 



" During certain portions of the growing season the winter-pruned trees of 

 certain varieties increase in trunk circumference more rapidly than trees that 

 have been both summer and winter pruned ; during other portions of the year 

 the reverse is the case. There seems to be a close correlation between increase 

 in trunk circumference at any period during the summer and the leaf area 

 possessed by the tree at that particular time. 



" In some varieties heavy early summer pruning has the effect of causing 

 those shoots remaining after the pruning to thicken and become more stocky 

 than those in trees that are not summer pruned. In other varieties the shoots 

 in the trees that are winter pruned only are the thicker and stockier. In all 

 the varieties studied the late shoot growth on the summer-pruned trees (i. e., 

 the shoot growth formed after the summer pruning) is comparatively slender. 



" Summer pruning of the type described affords a direct stimulus to fruit- 

 spur formation. Some of the buds on the basal portions of the shoots that are 

 left after the summer pruning almost invariably grow out into fruit spurs dur- 

 ing the latter part of the summer. Those that remain dormant during the 

 latter part of the summer are just as apt to develop into spurs the following 

 year as similarly situated buds on shoots that are not summer pruned. 



" The late summer-shoot growth of the summer-pruned trees is very produc- 

 tive of fruit spurs the season following its formation. A high percentage of 

 its buds develop into spurs. Herein, apparently, lies the chief gain in fruit- 

 spur production from the summer pruning. On the trees that are winter pruned 

 only, there is no growth to correspond with it. There is little or no relation 

 between the severity of the summer pruning and the number of spurs to each 

 unit of shoot length that remains. 



" Summer pruning of the type described affords a means of developing a 

 fruit-spur system in young apple trees earlier than is possible with the ordinary 

 method of winter pruning only ; it is estimated that its judicious use with va- 

 rieties bearing mainly upon spurs will enable the apple grower to bring his trees 

 into bearing approximately a year earlier than is otherwise possible, and still 

 maintain and develop a good framework. 



