296 



The Journal of Heredity 



properties of the soil, which may cause 

 certain trees to yield more than 

 others from year to year. 2. The 

 seedling root stocks used for apple 

 trees are extremely variable in vigor 

 and type of growth and may cause 

 much variation in yield of trees. 

 3. Variability in buds or scions of a 

 clonal variety may cause variability 

 in the performance of individual trees. 

 The various known factors which may 

 cause differences in the productivity 

 of trees of a clonal variety will be 

 considered in the above order. 



VARIABILITY IX PRODUCTIVITY, DUK TO 

 SOIL HETEROGENEITY 



If differences in productivity are due 

 to variable root stocks or variable 

 scions we would expect a random 

 distribution of high and low yielding 

 trees throughout the orchard. If soil 

 variability is the cause of differences 

 in performance we would expect to 

 find the high and low yielding trees 

 in rather definite groups. It is hardly 

 possible that soil differences can be so 

 local in extent as to effect the produc- 

 tivity of but a single tree. Frequently 

 an unproductive tree will be found 

 entirely surrounded by comparatively 

 productive trees. We have dug up 

 several of these trees and in every case 



Table III: Dislribulion of types of trees in Ben Davis Orchard 

 Showing in each block the total number of trees, number and percentage of Type 1, and number and 



percentage of Type 3. 

 Trees 



the root system of the unproductixe 

 tree was so interwoven with the root 

 systems of the productive trees that 

 they had to a great extent a common 

 feeding ground. In no case was the 

 isolated unproductive tree in appar- 

 ently poorer soil than the productive 

 trees. From this it seems apparent 

 that the isolated unproductive tree 

 cannot be due primarily to unfa\'orable 

 soil. On the other hand when high and 

 low yielding trees are grouped in defi- 

 nite areas it seems entirely probable 

 that these groups are due to soil 

 conditions. 



Ben Davis orchard No. 1 contains 

 37 rows with 29 to 37 trees per row. 

 The orchard was divided into twenty- 

 five blocks as shown in Table III. The 

 number of trees per block \'aries con- 

 siderably, due to missing or replanted 

 trees, or to variations in rows or trees 

 per row included in certain blocks. 

 The distribution of the extreme types 

 of trees is readilv observed in Table 

 III. 



It will be noted that the total 

 number of trees, the number and per- 

 centage of type 1 trees, and the num- 

 ber and percentage of type 3 trees 

 for each block are shown. Thus in 

 the block of trees including rows 1-8, 

 and trees 1-8, we find a total of fiftv- 



1-8 

 Rows 



9-16 



17-24 



25-32 



33-37 



