VARIABILITY IN LINKAGE OF CHARACTERS OF MAIZE 13 
The data from a single progeny at Lanham, Md., in 1924, shows 
a sensible correlation between the percentage of crossing over in 
two samples of the same heterozygous pollen as well as a correlation 
between the rate in upper and lower ears when the male parent is 
heterozygous. (Table 6.) 
These correlations can be interpreted only as resulting from fac- 
tors operating upon the male gametes, since in -the same material 
no correlation was found between the percentage of crossing over 
in the male and female gametes. The absence of a positive corre- 
lation in this latter instance shows that there are no genetic factors 
affecting both sexes in so far as this one progeny is concerned, and 
it also shows that environmental factors did not differentiate the 
individuals before the separation of the sexes. This conclusion 
derives further support from the lack of correlation between the 
percentage of crossing over on upper and lower ears where the 
female parent was heterozygous, thus indicating an absence of 
heterozygous genetic factors affecting the crossing over in one sex. 
An entirely different situation prevailed at Arlington, Va., in 
1923, with two progenies closely related to that grown at Lanham, 
Md., in 1924. Here high correlations were found between the per- 
centage of crossing over on butts and tips where the female parent 
was heterozygous or homozygous, as well as between the percentage 
of crossing over in upper and lower ears when the male was heter- 
ozygous and also between male and female gametes. From these 
correlations it is not possible to determine whether genetic or gen- 
eral environmental factors are the causal agents, but it is evident 
that one or the other or both are differentiating the individuals with 
respect to the rate of crossing over. 
A similar condition is indicated for the crossing over between B 
and Lg and G and Sh reported by Emerson and Hutchinson (6). In 
the case of each of these linked pairs, sensible correlations are found 
between the percentage of crossing over in the male and female 
gametes. 
Table 6. — Correlations between percentages of crossing over in two samples 
of gametes 
Correlation of percentage of crossing over between — 
Num- 
ber of 
plants 
Product 
moment 
coefficient of 
correlation (r) 
Cand Wx in two samples of same pollen, Lanham, 1924 
Cand Wx in male and female gametes, Lanham, 1924 
Cand Wx in upper and lower ears, female heterozygous, Lanham, 1924 
Cand Wx in upper and lower ears, male heterozygous, Lanham, 1924 
Cand Wx in butts and tips, female heterozygous, Arlington, 1923, progeny 1 
Cand Wx in butts and tips, female heterozygous, Arlington, 1923, progeny 2 
Cand Wx in butts and tips, male heterozygous, Arlington, 1923, progeny 2 
Cand Wx in upper and lower ears, male heterozygous, Arlington, 1923, progeny 1- 
Cand Wx in male and female gametes, Arlington, 1923, progeny 1 
B and Lg in male gametes with that of female, Emerson and Hutchinson (6) 
Cand Sh in male gametes with that of female, Emerson and Hutchinson (6) 
Cand Wx in upper and lower ears, male heterozygous, Ph 230L1 and L2R24 
Cand Wx in upper and lower ears, female heterozygous, Ph 230L1 and L2R24... 
0. 500±0. 145 
-. 333± . 147 
-. 328± . 146 
. 780± . 083 
. 6G2± . 058 
. 541 ± . 093 
. 962± . 016 
. 817± . 079 
.678± .062 
. 380± . 117 
. 597± . 091 
.249± .200 
. 483± . 091 
VARIABILITY OF CROSSING OVER NO GREATER IN MALE THAN IN FEMALE 
GAMETES 
As a means of determining whether the male gametes are more 
subject to environmental influences than the female gametes, the 
