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Bulletin 393 



to one or more centimeters of the previous season's spur growth; if the 

 spur growth was less than one centimeter, the spurs were classed as small. 



TABLE 33. Percentage of Large and of Small Spurs Setting Fruit on Limbs 

 WITH Diminished and on Those with Increased Sap Supply 



More fruit was produced on the large spurs than on the small spurs, 

 as would be expected from previously recorded observations. The small 

 spurs, as well as the large ones, are benefited by an increased supply 

 of sap, as is indicated b}^ the percentage gain. 



The term sap, as used in the preceding paragraphs, has reference 

 primarily to the watery solution taken up by the roots. No doubt some 

 of the organic food stored in the roots, and in the trunk and the main 

 limbs of the tree, would find its way into this solution before it reached 

 the spur. It would be difficult to state definitely which was the more 

 beneficial to the set of fruit — the water or the food material that it 

 contained in solution. The fact that the vigorous spurs have a larger 

 number of leaves and flowers than the weaker spurs, in itself suggests 

 that the buds in which they were formed were well supplied with organic 

 food. Miiller-Thurgau (1898) has shown that many fruits are borne 

 on limbs that have been girdled, while untreated limbs on the same tree 

 with equally heavy blooms set relatively few fruits. Chandler (19 13) 

 has demonstrated that the sap derived from the cortex and the bark 

 of girdled apple twigs is much denser than sap from similar limbs recei\dng 

 no treatment. Gourley (19 15) shows that more food is stored in fruiting 

 than in non-fruiting spurs. There can be little doubt that an abundance 

 of stored food is one of the factors favoring the setting of fruit. On the 

 other hand, it must be borne in mind that heavy spurs usually have 

 a large diameter of conducting tissue, which insures a good sap supply. 

 Furthermore, the observations recorded above indicate that an abundant 



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