298 
Journal of Agricultural Research voi. xxvii, No. 5 
Comparing the differences between Egyptian and Upland cotton in 
the first and second series of determinations, we note that the differences 
between the differences (Table XIII, column 8) show that the second 
series has a numerically somewhat larger difference 17 in one of the three 
fundamental series, row 1 and 5, and a somewhat smaller difference in 
the other two, rows 3 and 7 and 2, 4 and 6. The difference between 
these differences can hardly be considered significant in comparison with 
their probable errors. The ratios range from 0.5 to 3.6. 
It is clear, therefore, that the differentiation between the Egyptian 
and the Upland types with respect to the hydrogen-ion concentration of 
their tissue fluids can not be asserted to become greater with the advance 
of the season. This result for acidity, with respect to which differen¬ 
tiation has been shown to exist, is therefore in agreement with the ratio 
of specific electrical conductivity to freezing point depression, for which 
no differentiation has been demonstrated between the types. It is 
not in agreement with the results for freezing point depression, A, or 
specific electrical conductivity, k , both of which showed an increase in 
the differences between the Egyptian and Upland cotton with the ad¬ 
vance of the season. 
In referring to the advance of the season, we must remember that 
there are but two groups of data upon which conclusions concerning 
seasonal changes may be based. Caution must, therefore, be used in 
attributing a seasonal significance to these results. The term is used 
here merely as a means of conveniently describing the actual facts. 
PRESENTATION AND ANALYSIS OF DATA FOR HYBRIDS 
The frequency distributions of the various physicochemical measure¬ 
ments made upon the hybrid in 1921 have been presented in tables 
VI-IX. For a more detailed comparison of the properties of the fluids 
of hybrid and parental forms we must resort to a consideration of the 
differences in the individual constants and in the statistical constants 
derived from these individual measurements. 
The results for the preliminary measurements made in 1920 will first 
be given. The data of the more detailed studies made in 1921 will then 
be presented in the form of statistical constants. 
PRELIMINARY STUDY IN 1920 
We were able to secure the following determinations: 
Acala X Pima F x (29) 18 was taken on August 14. While not immediately 
associated with samples (1) = Egyptian and (2) = Upland, it may be 
most nearly compared with them. On August 18 Pima Egyptian X 
Upland F x (30) was taken between two rows of Pima (31). On the 
same date Pima Egyptian X Upland F x plants (32) were also taken in 
close proximity to Holdon Upland plants (33). On August 22 Pima 
Egyptian X Upland F x (34) was taken in comparison with Pima Egyptian 
(No. 25) and Holdon Upland (No. 26). In the same border we were 
so fortunate as to obtain a progeny of Acala X Pima F x (35) lying between 
17 Since the differences between the two types of cotton in column 8 are so taken as to have a negative 
sign when Ph is lower for Egyptian than for Upland cotton, a negative sign for the difference between the 
differences indicates that the difference is numerically larger in the second series of determinations. 
18 The numbers in parentheses are those of our samples of hybrid tissues. The number of the determi- 
dation on the parent type is also given for the differences. The actual constants for these parent type 
numbers will be found in Table I. 
