702 
Joumal of Agricultural Research voi. xxviii, No. ~ 
Table VI.— Correlation between the chlorid content of associated plants or groups of 
plants of Egyptian and Upland cotton as grown at Sacaton , im., in 1922-23 
Correlation for first series 
Correlation for second 
series. 
Correlation 
coefficient 
and probable 
error 
rd=E f 
Ratio 
of cor¬ 
relation 
to prob¬ 
able 
error 
r/E r 
Correlation 
coefficient 
and probable 
error 
rdbEr 
Ratio 
of cor¬ 
relation 
to prob¬ 
able 
error 
r/E r 
First comparison of Fima Egyptian and Meade and 
Acala Upland cotton, 1922 (B): 
Cnp-filafiinri hfifrEPAAri Pima ftpri x _ 
0.6702=fc0.0454 
. 6844=fc . 0432 
. 5144=1= .0723 
.3372=1= .0725 
14.76 
15.85 
7.11 
4.65 
0.6029^=0.0524 
.6030=1= .0520 
11.50 
11.59 
Correlation hatweap Pima and A.. - . 
Second comparison of Pima Egyptian and Meade 
Upland cotton, 1922 (C): Correlation between 
Puna and Meade_-_______ 
Comparison of Pima Egyptian and Lone Star Upland 
cotton, 1923 (D): Correlation between Pima and 
Lone Star___ 
.1698=1= .0794 
2.14 
The coefficients of correlation, r, measuring the relationship between the 
chlorid content of associated plants or subrows of plants, are given with their 
probable errors in Table VI. 
The coefficients for the cultures of 1922 are of about the same order of magni¬ 
tude as those already published for osmotic concentration and specific electrical 
conductivity in cultures of Pima Egyptian, Meade and Acala Upland and hybrid 
cotton grown at Sacaton in 1921 (5). The constants for Pima Egyptian and 
Lone Star Upland cotton studied in 1923 are much lower. This is presumably 
due to the greater uniformity of the half of the plot upon which this culture 
was grown. 
The fact that the chlorid content of associated plants is correlated is not a 
matter of merely physiological interest. It must be considered in determining 
the statistical significance of the differences between the varieties. The fact that 
the variability of the constants is due largely to the heterogeneity of the sub¬ 
stratum makes it essential that the constants for any two varieties compared be 
based on plants which have grown in the closest association practicable, and that 
the constants compared comprise only individuals of the same pair. 
Since the two types to be compared were grown in close association in a large 
number of subplots distributed over the cultural area, both were subjected to the 
influence of similar soil conditions. This tends to reduce the probable errors of 
the difference between the mean chlorid content of the Egyptian and Upland 
types as based on the whole series of determinations available for each culture 
and series of samples. These probable errors may be calculated from the stand¬ 
ard deviation of the difference between associated determinations as obtained 
from the formula 
<r 2 (p—„)=O' 2 P +<r 2 «_2r PU <r p <r tt , 
or by actually determining the individual differences between the Pima and 
Upland determinations of the associated plants and calculating the standard 
deviations of these differences directly. 
Table VII presents the mean chlorid content in terms of grams of Cl per liter 
of tissue fluids for the Egyptian and Upland varieties compared in the various 
cultures. N denotes the number of pairs of determinations. The probable 
errors of the means of the individual series have been calculated by the usual 
formula. The standard deviations are not published since variability of chlorid 
