72 POMOLOGY 



however, that some varieties, more than others, are incUned 

 to estabUsh as a habit either amiual, biennial, or irregular 

 bearing. 



Roberts ^ has pointed out that there is a close relation- 

 ship between fruit-bud formation and spur growth. For 

 example, with the Wealthy apple under Wisconsin conditions, 

 fruit-buds are formed freely when the spurs make a growth 

 of one-eighth to three-eighths of an inch in length, and when 

 the growth is much less or greater, flowering is partially or 

 entirely suppressed. In the "off" year when 85 or 90 

 per cent of the spurs formed fruit-buds, this amount of 

 growth was common, but in the "on" year it was consistently 

 shorter, thus producing a cycle or a biennial bearing condition. 

 This observation is comparable to the one already discussed, 

 namely, the alternation in size of leaves in the "on" and 

 "off" years with the Yellow Transparent (and other) 

 apples. While a crop of fruit usually checks vegetative 

 extension, leaf size, and often fruit-bud formation, such 

 check may also be due to other causes, such as the weather 

 or cultural conditions, and, therefore, it is not necessary for 

 a heavy crop of fruit to precede the establishment of the 

 biennial bearing habit. 



As a practical solution of this problem, three possible 

 procedures may be suggested. First, when the trees are 

 fruiting heavily and consequently making less than the 

 requisite growth (say less than one-eighth to three-eighths 

 inches) , the trees might be stimulated by an early application 

 of available nitrogen. Thinning the fruit has not proved 

 effective in accomplishing this result, as explained in Chapter 

 VI. Second, during the off year when the growth is such as 

 to be conducive to flower formation, nitrogen may be added 

 in order to push the trees into an " over vegetative " condition 



1 Roberts, R. H. Off-year apple bearing. Wis. Agr. Exp. Sta. 

 Bull. 318. 



