62 Bulletin 393 



on long twigs. No analyses are available to show that such a condition 

 actually exists. 



In several cases, the spurs arising from 1913 twig growth set more fruit 

 than did spurs arising from older wood. In other cases, however, spurs 

 on older twigs were more fruitful than those on younger growth. This 

 fact suggests that the ability of a bud to develop into a fruit-setting 

 spur is determined to some extent during the year when it is formed in 

 the axil of a leaf. It should be mentioned, in this connection, that many 

 limbs have no flower-bearing spurs on a given year's growth, whereas 

 such spurs are borne on younger and on older wood of the same limb. 

 Then, too, the proportion of buds that develop into fruiting spurs varies 

 with the different year's growth on the same branch. 



Apparently the age of the spur alone, at least from the second to the 

 fourth or the fifth year, has little influence on its fruitfulness. Spurs 

 arising from wood several meters from the periphery of the tree would 

 generally be in a less desirable position so far as exposure to light and free 

 circulation of air are concerned. This condition would probably have an 

 unfavorable influence on the nutrition of the fruit bud. 



SET OF FRUIT ON SPURS FORMED ON DIFFERENT PARTS OF A GIVEN YEAR's 



GROWTH 



The vigor of the individual buds found on the twig growth of a given 

 year varies considerably. This can be determined by observing the fate 

 of the buds the year after they have been formed. In most of the varieties, 

 buds near the beginning, and in many cases those just before the end, 

 of a year's growth remain dormant (Koopmann, 1896). If a year's growth 

 happens to be from thirty to forty centimeters, a third zone of weak 

 buds may be found near the center of that particular year's growth. 

 The transition from dormant buds to those that produce strong spurs, 

 or even short twigs, is usually, but not always, a gradual one. The 

 strongest spurs are generally found just before the terminal zone of 

 dormant buds, and before the middle zone if there is one. The leaves in 

 the zones bearing weak buds will usually be the first to turn yellow and 

 fall off if the twigs are removed from the tree and placed in beakers 

 containing water. Such leaves likewise are the first to be shed in the 

 autumn. 



Just what causes these variations in bud vigor is not definitely known. 

 They are found even in upright twigs growing at the top of the tree, 

 where light conditions for the different buds are approximately the same. 

 The nutrient supply available at the time of formation of the individual 

 bud may determine its vigor. It is probable that the water supply from 



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