STATE POMOLOGICAL SOCIETY. 69 



In Table V, the most marked exception to the present rule 

 appears in the case of the phosphates, especially in the lower 

 section of the table. This may be connected with the fact that 

 old wood especially is very low in phosphoric acid, as shown 

 in Table I, and our present definite growth determinations are 

 based upon increase in trunk girth alone. On twig growth, 

 however, our observations indicate that phosphate additions 

 have been very helpful, particularly in the Brown orchard, a 

 fact which tends to bring it in line with the general rule just 

 stated. 



The Control of Average Sise. — So far as fertilization is 

 concerned, manure and potash are the only materials that 

 have consistently benefited size. This influence of manure is 

 doubtless very largely due to its mulching effect, since moist- 

 ure makes up about 84.6 per cent of this fruit, on the average.* 

 The potash influence also, so far as it is a definite benefit, is 

 probably exercised through the same medium, inasmuch as 

 potash is credited with some ability to increase the osmotic 

 power of the cells and thus enable them to compete more suc- 

 cessfully for whatever water is present. 



There is also a distinct possibility that the apparent benefit 

 of potash on size may be largely due to the fact that it is as- 

 sociated with much lower yields than the other materials, 

 especially nitrogen. Conversely, the failures of the latter to 

 increase size may likewise be due to association with markedly 

 increased yields. 



This brings out the general proposition to which we have 

 called definite attention elsewhere, t viz.. that with a normal 

 moisture supply and sufficient growing season, the dominant 

 influence controlling size in apples is the numlber 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 



* See Table XVIII in the writer's article in the Annual Report uf 

 the Pennsylvania Agricultural Experiment Station for 1910-11, p. 435. 

 t See article referred to in footnote 3, pages 500-503. 



