44 
BULLETIN 1468, XT. S. DEPARTMENT OF AGRICULTURE 
It should be noted in this connection that in the same two series 
there is a difference in reciprocals with respect to the percentage of 
white. In the repulsion series in the work of Emerson and Hutchi- 
son (#, Table, S) there is a significantly lower percentage of white 
when the male is the heterozygous parent (3.2±0.56 per cent), and in 
the coupling series (#, Table If) there is a lower percentage of white 
when the female is the heterozygous parent (4.0±1.2). These differ- 
ences statistically are of greater significance than the differences in 
crossing over. 
In view of wide and significant fluctuations in the rate of cross- 
ing over that can not be ascribed either to genetic or to know environ- 
mental causes, it seems probable that the much smaller differences 
between the sexes are of the same nature. Until the causes of the 
variations in crossing over are better understood it will be unsafe to 
associate differences in the crossing over of reciprocals with differ- 
ences in sporogenesis. 
DIFFERENCES IN CROSSING OVER IN RECIPROCALS WHEN LINKAGE IS NOT OPERATIVE 
In making comparisons between the rate of crossing over in male 
and female gametes where linkage was involved, it was thought de- 
sirable to assemble the same sort of data for cases where no linkage 
was possible. 
Table 26 shows the results of reciprocal crosses between white- 
horny plants heterozygous for waxy (e c Wx wx,) and colored-waxy 
plants heterozygous for color (Go wx wx). The totals show there 
is a slight but insignificant difference between the reciprocals in the 
proportion of the crossover to noncrossover classes. 
Table 26. — Reciprocal crosses of colored waxy (G c wx wx) X white horny 
(c c Wx wx) 
White-horny $ 
Colored-waxy 9 
Difference 
(colored 
Cross designation 
Number 
of seeds 
Percentage 
of crossovers 
Number 
of seeds 
Percentage 
of crossovers 
waxy— 
white- 
horny) 
3882X3776 . 
290 
180 
515 
150 
61 
97 
414 
592 
224 
447 
505 
585 
438 
419 
53. 9±1. 98 
52. 3±2. 50 
47. 5±1. 48 
52. 5±2. 74 
33. 4±4. 07 
49. 6±3. 42 
47. 8=1=1. 65 
54. 7±1. 38 
49. 6=1=2. 24 
53. 4±1. 59 
50.9±1. 50 
49. 9±1. 39 
51. 5±1. 60 
52. 3±1. 64 
189 
198 
538 
72 
389 
26 
510 
445 
450 
628 
416 
360 
550 
256 
50. 9±2. 45 
49. 3±2 39 
46. 9±1. 45 
40. 8±3. 90 
50. 5±1. 39 
44. 9±6. 56 
47. 5±1. 49 
52. 5±1. 59 
51. 1±1. 59 
51. 2=1=1. 34 
48. 1±1. 65 
47. 7±1. 77 
49. Odzl. 43 
49. 7±2. 10 
-3. 0=b3. 15 
3885X3787 
-3. 0±3. 46 
3888X3778 
-. 6=1=2. 07 
3892X3784 
— 11. 7±4. 76 
3895X3787-2 
+17. 1=1=4. 24 
3898X3793 
-4. 7=1=7. 40 
3900X3789 
-. 3=1=2. 28 
3907X3802 
-2. 2=1=2. 10 
3907-2X3801 
+1. 5=1=2. 75 
3909X3804 
-2. 2=1=2. 08 
3916X3808 
-2. 8±2. 23 
3916-2X3808-2 
-2. 2=1=2. 25 
3919X3806 
-2. 5=1=2. 14 
3922X3803 
-2. 6=1=2. 66 
-1.50=1= .65 
This result was anticipated, but the array of differences is some- 
what disturbing. Inspection will show that in 12 of the 14 pairs 
of reciprocals the proportion of colored-waxy and white-horny seeds 
was higher when the female parent was white horny. Of the two 
exceptions, one may be a chance fluctuation, but the other robs the 
array of its statistical significance. This plus difference results 
