Abscission of Flowers and Frvits of the Apple 8i 



supply of sap to spurs inadequately provided with storage tissue increases 

 the ability of such spurs to set fruit. 



FRUIT SETTING AS INFLUENCED BY VARYING AMOUNTS OF LEAF SURFACE 



ON THE FLOWER-BEARING SPUR 



As previously shown, limbs with small leaves have a smaller proportion 

 of fruitful spurs than similar limbs with large leaves. The area of the 

 leaf surface seems to be closely correlated with the vigor, or weight, of 

 the spur, which in turn shows a relation to the diameter of the cylinder 

 of conducting tissue thru which the sap reaches the developing spur. 

 The leaves might have several effects: they might assist in drawing water 

 to the spur — the "pulling power of transpiration"; they might provide 

 increased nourishment for the developing tissue; they might prove 

 detrimental during conditions favoring incipient drying, by actually 

 withdrawing moisture from the young flower or fruit. (Chandler, 191 5). 

 In order to gain some information regarding the influence of the bud 

 leaves on the setting of fruit, the following experiments were carried out: 



In the first experiment, a number of pairs of similarly located and 

 equally vigorous spurs were selected. The vigor of the spurs was 

 determined by the amount of leaf surface, and also by noting the length 

 of the previous season's growth. The spurs of each pair were taken 

 from the same parent branch and from points within a few inches of 

 each other. Vigorous spurs only were selected because previous obser- 

 vations had shown that such spurs have the greatest tendency to set 

 fruit. The importance of having spurs of similar location and vigor is 

 obvious. 



One spur of each pair was entirely defoliated, while the other sensed 

 as a check, receiving no treatment. The leaves on the former were 

 removed just before the blossoms opened in the spring of 19 16. The set 

 of fruit on the spurs was determined during the latter part of August. 

 Unfortunately, many pairs had to be discarded because of aphid injury'. 

 Only healthy spurs were considered. The data are recorded in table 34. 



The figures indicate that some of the defoliated spurs bear fruit, but 

 the percentage of these is very much less than in the case of normal spurs. 

 The high percentage of fruitful spurs recorded for the latter class reflects 

 the influence of vigor. 



The object of the next experiment was to determine the effect of partial 

 and of complete defoliation of flower -bearing spurs on the setting of 

 fruit. Several lots, each consisting of three similarly located and equally 

 vigorous spurs, were selected. As a rule, vigorous spurs have from seven 

 to ten first, or bud, leaves. One spur in each lot ser\^ed as a check; the 



195 



