16 
BULLETIN 1468, U. S. DEPARTMENT OF AGRICULTURE 
The classification obtained from these divisions furnishes data 
from which the relative variability in percentage of crossing over 
of the two halves of the ear can be measured. 
In all three cases (male and female gametes from one progeny 
and female gametes from the other) crossing over proved to be 
more variable in the tip than in the base of the ear, but in none 
of the cases was the difference significant. The mean difference 
(V^W/TN) is 1.22+0.56. 
It would 'seem, therefore, from the present data that one part of 
the ear is as variable as the other with respect to the rate of crossing 
over. The data are presented in Table 9. 
Table 9. — Comparison of variability (cso) of percentage of crossing over in the 
tip and the base of the ear 
Num- 
ber of 
ears 
Tip 
Base 
Progeny 
Per- 
centage 
of cross- 
overs 
a 
0m 
Per- 
centage 
of cross- 
. overs 
<r 
O"60 
Difference 
(<7"m tip— 
0"k> base) 
Female gametes: 
Dh 41SL3L1C5L3L1R23.— 
Dh 416L3L1C5L3L2R23— . 
Male gametes: 
Dh 416L3L1C5L3L2R23..- 
43 
26 
10 
22.10 
24.02 
27.28 
6.19 
7.62 
7.05 
7. 46±0. 54 
8. 82± . 83 
7. 90±1. 19 
20.68 
21.49 
28.19 
5.27 
5.53 
7.10 
6. 51±0. 47 
6. 72± . 63 
7. 88±1. 19 
0. 95±0. 70 
2. Mfcfcl. 04 
. 02±1. 68 
CROSSING OVER GENERALLY LESS VARIABLE IN SEVERAL SAMPLES OF THE SAME 
INDIVIDUAL THAN IN SINGLE SAMPLES FROM SEVERAL INDIVIDUALS 
In narrowing the field of factors that might bear a causal rela- 
tionship to the variation in crossover percentages, it became of inter- 
est to compare the variability as measured in a progeny of plants 
with that of several measures of individual plants from the same 
progeny. 
It seldom happens that a single plant serves as a parent for more 
than two ears, but the records afford two cases where plants served 
as male parents in four and five pollinations. 
Many progenies are available where single plants have functioned 
twice as male parents, and two progenies furnish material where 
single plants have functioned twice as female parents. 
These paired samples can be used to calculate the relative vari- 
ability of samples from single plants as compared with that of 
several plants. If two samples of gametes from an individual are 
as unlike, on the average, as the means of the individuals, then the 
standard deviation (<r) of the differences between pairs should equal 
the standard deviation of the sum. 
These comparisons have been made for a number of progenies and 
various sorts of paired samples in Table 10. 
For some of these progenies the same relationship is indicated by 
the correlation between samples as shown in Table 6 (p. 13). 
The first five entries in Table 10 are drawn from upper and 
lower ear groupings and are limited to pollinations made on the 
same day. Those where the male parent is heteroz3^gous are further 
limited to the same double recessive parent, thus obviating any 
