294 



The Journal of Heredity 



Table I: Average yields of the types of trees for 1914-18. 

 Mean Yields in lbs. of fruit. 



(881) more than one-third produced 

 less than one barrel per tree, due 

 largely to the presence of unproductive 

 types of tree.s. 



In the table given above it is 

 evident that the trees of type 1 are the 

 most productive and that the produc- 

 tivity decreases as the intermediate 

 types approach type 3. It is possible 



to measure accurately the degree of 

 correlation between tree type and yield 

 by determining the correlation ratio. 

 These measures of correlation are 

 shown in Table II for the years 1914- 

 18. 



The correlation of .50 to .70 indi- 

 cates that tree type is a reliable indica- 

 tion of the probable yield of the tree. 



Table II: Ben Davis Apple Orchard. 8S1 trees. 

 Correlations between type, yield and circumference. 



Correlation between type and yield 



Correlation between type and circiiinference 



Correlation between cirruniference and yield 



In other w(jr(ls we would, in general, 

 be justified in using tree type as a 

 means of judging which trees arc 

 uniiroductive and unprofitable. 



The correlation ratios between type 

 of tree and circumference of trunk are 

 also determined. The high degree of 

 correlation (see Table II) between 

 type and circumference indicates that 

 type 1, or productive trees, are in 

 general the largest trees, and that the 

 type 3 or unproductive trees are as a 

 nile small. These results indicate that 

 vield is closcK' associated with the 



size as well as t>pe of tree. The 

 relation between circumference of trunk 

 and yield is shown in Table II. Both 

 the correlation coefficients and corre- 

 lation ratios are high, indicating that 

 yield al.so is closely correlated with size 

 f)f tree. The question immediately 

 arises: to what extent are the th'flereiices 

 in >ield of the various types tlue to 

 diflerences in the size of the trees ot 

 each type? By determining the corre- 

 lation between t>pe and \ield with the 

 tree circumference held constant little 

 or no cortHlatioii betwi-en t\pe and 



