Feb, 2, 1934 
Tissue Fluids in Cotton 
3 21 
We may turn again to Table XXIV for a comparison of the magnitudes 
of the correlations for specific electrical conductivity, ratio of conductivity 
to freezing-point depression, and hydrogen-ion concentration. 
In the first series the correlation for specific electrical conductivity 
is in every instance higher than that for the ratio of conductivity to freez¬ 
ing-point depression. In the second series the same relationship holds 
in only 7 of the 10 comparisons. The differences in both first and second 
series are generally low. We have no explanation of this result to 
suggest. 
A comparison of the coefficients of correlation for hydrogen-ion con¬ 
centration with that for specific electrical conductivity indicates that in 
the first series of determinations the correlation for conductivity is higher 
than that for hydrogen-ion concentration, whereas in the second series 
of determinations the reverse is true. This result is substantiated by a 
comparison of the coefficients for the ratio of conductivity to freezing- 
point depression with those for hydrogen-ion concentration. 
The determination of the environmental (soil or atmospheric) or the 
internal conditions to which these differences are due presents a problem 
for future investigation. 
SUMMARY AND CONCLUSIONS 
While this paper is in substance a contribution to the comparative 
physiology of Egyptian and Upland cotton, its purpose has been broader. 
It is one of a series of investigations which have been undertaken with 
the conviction that the relative capacity for growth and production 
of different crop plants under special conditions ultimately depends 
upon intrinsic morphological and physiological differences, and that in 
our attempts to secure varieties of crop plants which may be success¬ 
fully grown under particularly stringent environmental conditions (such 
as those of extremes of temperature, or of aridity of the soil or atmos¬ 
phere, or of the concentration or reaction of the soil solution) we will in the 
long run make the most rapid and certain progress by determining the 
particular variables which fit the plant for growth under these con¬ 
ditions. With a working knowledge of these variables, based on inves¬ 
tigations of native vegetations and of crop plants, it will be possible to 
select varieties which seem most suitable for growth under peculiar 
environmental conditions. 
The present investigation has been limited to osmotic concentration, 
specific electrical conductivity and acidity in terms of hydrogen-ion 
concentration in the leaf-tissue fluids of Pima Egyptian and of Meade 
and Acala Upland cottons and of those of the hybrid between Pima 
and Meade cotton as grown under irrigation in southern Arizona. This 
has been in part because the technique for work with these variables is 
in a more satisfactory state of development than that for others which 
may be of importance. The limitation has, however, been primarily 
because investigations on natural vegetation have indicated a close rela¬ 
tionship between the first two of these variables and the dryness and 
salinity of the substratum. 
The statistical constants for sap properties are based on a large number 
of determinations on plants grown in 1921 on subplots at the Cooperative 
Testing Station, Sacaton, Ariz. The determinations were made in two 
series, the first based on collections of tissue made from August 6 to 
August 16; the second on samples of tissue gathered from August 19 to 
