68 



the dominant influence controlling size in apples is the number of 

 fruits on the tree, after this number has passed a certain optimum 

 or "critical point." This point, however, is relatively high, our 

 data showing that even on trees up to 15 years of age, little or no 

 correlation appeared until the number of fruits had reached 1,400 

 or more per tree. Above this point, proper thinning is the most 

 important means of increasing the size of the fruit. Below it, 

 the size can usually be markedly affected by moisture supply, cul- 

 tural methods, manure and possibly by fertilizers, — especially those 

 rich in potash. The latter factors may also co-operate in such a way 

 as to materially raise the critical point. In general, however, proper 

 thinning and moisture conservation are the most important means 

 of improving fruit size. 



The Control of Fruit Color.— In Table V, it will be observed 

 that none of the fertilizer treatments has resulted in any marked im- 

 provement in color. Slight and irregular benefits are shown by 

 potash and some of the phosphate applications, but nothing of any 

 importance. The same is true of iron applications so far as ex- 

 perimental evidence is concerned. 



These facts again lead up to the general propositions that color 

 in apples can not be materially increased by fertilizer applications, 

 and that the red colors of apples are essentially dependent upon 

 maturity and sunlight. Conditions that tend to increase one or 

 both of the latter factors, such as late picking, open pruning, light 

 soils, and sod culture tend to increase the red color. Opposite con- 

 ditions decrease it. 



These propositions make it clear why the nitrates and manure 

 apparently injure color. It is simply done by retarding maturity 

 and diminishing the available sunlight as a result of the increased 

 density of foliage. To determine the truth of this, in 191 1 we left 

 the fruit on the nitrate plots in the Johnston orchard, until it had 

 reached approximately the same degree of maturity as that at- 

 tained by the checks when their fruit had to be picked on account 

 of dropping. The delay required was fully three weeks, — from 

 September 29th to October 19th, — and even then the latter fruit 

 picked much harder than that on the checks, besides showing a 

 much lower percentage of drops. The amount of color on the 

 nitrate plots at the latter date also was actually greater by 10% 

 than that shown on the checks at their picking time. 



The occasional marked increase on color as a result of spray- 

 ing is largely explainable on similar grounds. The sprays reduce 

 the worminess and thus enable the fruit to remain longer on the 

 tree. It also may reduce somewhat the amount of foliage as a result 

 of spray-injury thus permitting more light to reach the fruit. In 

 general, however, in improving color, chief reliance must be placed 

 on those methods that tend definitely to secure fuller maturity on 

 the tree and to get the maximum amounts of light to the fruit. 



