60 
BULLETIN 146S ? V. S. DEPARTMENT OF AGRICULTURE 
Table 37. — Correlations showing the association of percentage of crossing over 
with number of seeds 
Progeny 
Characters correlated 
Num- 
ber of 
ears 
Product 
moment 
coefficient of 
correlation(r) 
Dh 416: 
L3L1C5L4L1L24, re- 
ciprocals. 
Do 
Crossing over in ovules and number of seeds in heterozy- 
gous parent. 
Crossing over in ovules and number of seeds in homozy- 
gous parent. 
Crossing over in pollen and number of seeds in heterozy- 
gous parent. 
Crossing over in pollen and number of seeds in homozy- 
gous parent. 
Crossing over in pollen and crossing over in ovules 
Number of seeds in heterozygous parent and number of 
seeds in homozygous parent. 
Crossing over in ovules and number of seeds in heterozy- 
gous parent. 
Crossing over in pollen and number cf seeds in homozy- 
gous parent. 
Crossing over in ovules and number of seeds in heterozy- 
gous parent. 
Crossing over in pollen and number of seeds in homozy- 
gous parent. 
Crossing over in ovules and number of seeds in heterozy- 
gous parent. 
Crossing over in pollen and number of seeds in homozy- 
gous parent. 
Crossing over in ovules and number of seeds in heterozy- 
gous parent. 
Crossing over in ovules and number of seeds in homozy- 
gous parent. 
Crossing over in pollen and number of seeds in heterozy- 
gous parent. 
Crossing over in pollen and number of seeds in homozy- 
gous parent. 
Crossing over in pollen and crossing over in ovules 
Number of seeds in heterozygous parent and number of 
seeds in homozygous parent. 
Crossing over in ovules and number of seeds in heterozy- 
gous parent, 
Crossing over in ovules and number of seeds in homozy- 
gous parent. 
Crossing over in pollen and number of seeds in heterozy- 
gous parent. 
Crossing over in pollen and number of seeds in homozy- 
gous parent. 
Crossing over in pollen and crossing over in ovules 
Number of seeds in heterozygous parent and number of 
seeds in homozygous parent. 
_ 
17 
17 
17 
17 
17 
17 
52 
55 
17 
37 
21 
19 
19 
19 
19 
19 
19 
19 
20 
20 
20 
20 
20 
20 
0. 338±0. 15 
. 371± . 15 
-. 012± . 17 
Do 
Do 
Do 
— 186± 16 
Do . 
L3L1C5L4L1L24, all 
ears. 
Do . 
. 332± . C8 
126± 09 
L3L1C5L4L23, all ears. 
Do 
-. 054± . 17 
030± 11 
Dh 417: 
L1L2L1L2L23, all ears. 
Do 
. 208± . 14 
. 091± 16 
Emerson and Hutchison 
(6): 
B-Lg, reciprocals 
Do 
. 194± . 16 
— . 459d= . 13 
Do- 
— . 199± . 16 
Do 
— . 337± . 14 
Do- 
. 262± . 15 
Do 
. 012± . 16 
C-Sh, reciprocals 
Do 
-. 129± . 15 
. 041± . 15 
Do 
— .091± .15 
Do 
. 568± . 10 
Do 
. 168± . 15 
Do 
-. 206± . 14 
DISCUSSION 
Cytological examination shows that the reduction divisions, in the 
strains of maize under consideration, occur approximately three 
weeks before the flowers mature. The period over which these divi- 
sions take place, though not well delimited, is about four days. Any 
factors which affect the proportion of crossover to noncrossover 
gametes subsequent to the reduction division would of necessity 
operate to bring about a differential death rate either of gametes 
or of zygotes. 
If the actual rate of crossing over is susceptible to alteration 
through the influence of environmental factors, such factors must 
be operative three or four w T eeks before anthesis. Further, if the 
actual rate of crossing over can be affected only at the time of the 
reduction division, the period during which environmental factors 
can operate effectually is limited to a period of three to five days. 
