VARIABILITY IN LINKAGE OF CHARACTERS OF MAIZE bf) 
RATE OF CROSSING OVER SIMILAR IN FIRST AND LAST POLLEN SHED 
Eight plants are available from a single progeny from which the 
first pollen shed was used and a further sample taken after a lapse 
of several days. The data from these plants, shown in Table 34, can 
be used to test any change associated with the age of the plant. 
The mean time difference between the first and last samples of 
pollen was 4.66 days, and the rate of crossing over was 0.48 ±0.86 
per cent greater for the early samples than for the late ones. This 
difference can not be considered significant, and with the popula- 
tion of eight plants a difference of 3 per cent could have been 
detected. 
A further test of changes in the rate of crossing over associated 
with the increase in age of the parent is found in a second progeny 
where each of seven plants functioned twice as male parents with a 
lapse of one da}^ or more in time between the two applications of 
pollen. These cases are also shown in Table 34. In this progeny the 
greater rate of crossing over is found in the late pollen, though the 
difference is not significant. 
Table 34. — Percentage of crossing over in first pollen shed compared with that 
shed at a later date 
Early pollen 
Late pollen 
Difference 
Heterozygous plant 
Num- 
ber of 
seeds 
Per cent- 
age of 
crossovers 
Num- 
ber of 
seeds 
Per cent- 
age of 
crossovers 
Per cent- 
age of 
crossovers * 
Num- 
ber of. 
days 
Progeny Dh 416L3L1C1L1L2-1-L23: 
No. 2507 
350 
719 
1,068 
278 
402 
462 
337 
1,211 
17. lil. 60 
37. 8il. 22 
36. 2i . 99 
27. 7il. 81 
21. 6il. 49 
33. lil. 39 
19. Oil. 63 
27. Oi . 85 
18 
71 
151 
606 
903 
493 
413 
226 
11. Ii7. 05 
32. 4i3. 55 
34. 4i2. 42 
20. 6il. 21 
22. 9i . 94 
30. 7il. 40 
22. 8il. 47 
28. 7i2. 03 
6.0 i7.26 
5.4 i3.75 
1.8 ±2. 62 
7. 1 i2. 18 
-1.3 ±1.77 
2.4 ±1.97 
-3.8 il. 68 
-1.7 i2. 20 
9.5 
No. 2518 
2.0 
No. 2520. 
3.0 
No. 2514 
4.5 
No. 2509 
5.0 
No. 2519 
5.5 
No. 2510. 
5.5 
No. 2511 . _ 
2.0 
. 48 i . 86 
4.66 
61 
606 
566 
602 
599 
224 
256 
11. 5i2. 76 
19. 6il. 09 
16. Oil. 03 
16. lil. 00 
29. Oil. 18 
18. 7il. 75 
19. 9il. 68 
595 
788 
516 
210 
834 
602 
811 
18. 8il. 04 
17. 3i .91 
16. 3±1. 09 
19. 7il. 85 
27. 6il. 04 
23. 4il. 16 
16. 9i . 88 
Progeny Dh 416L3L1C5L3L1R23: 
No. 5901 
-7.3 i2.94 
2.3 ±1.41 
-.3 ±1.51 
-3.6 ±2.10 
1.4 ±1.53 
-4.7 ±2.10 
3.0 ±1.90 
4 
No. 5902 
6 
No. 5903 . . 
1 
No. 5916 
4 
No. 5919 
6 
No. 5938 
3 
No. 5941 ._._ 
6 
-. 146± . 871 
4.3 
i 
1 Minus sign indicates those cases where more crossing over occurred in the late pollen. The probable 
error given has been corrected for the size of the population. 
Combining the two progenies, the mean difference becomes 
0.128±0.604 per cent, with a greater crossing over in the early pollen. 
This difference, of course, is not significant, and a consideration of 
the probable errors shows that a difference of 2 per cent could have 
been detected. 
There would seem to be no reason to believe that the rate of 
crossing over between C and Wx changes appreciably with the ad- 
vance of time, even though the period over which the gametes are 
forming probably is as long as the period involved in the present 
comparisons. 
From the mean difference between these paired ears it is not 
possible to determine whether environmental factors operative at 
