502 
Journal of Agricultural Research 
Vol. XXVII, No. 7 
Table XI .—Petal spot grade of pairs of plants selected in each parental progeny of 
IQ 22 as representing the extremes of the progeny and means of the progenies of these 
p 1-ants grown in 1923 
Progeny and selection. 
Petal spot 
grade of the 
individual 
selected in 
1922. 
Mean of its 
progeny grown 
in 1923. 
SPOTTED PARENTAL FAMILIES 
[No. 2. 
! 'y 
i /• 3 
j 7 - 9 
8. I±o. 04 
8. 0± . 05 
I2_I nNo. 23. 
Difference. 
1 
.6 
. I± • 064 
fNo I7. 
7. 2 
8 . 0 
8. i ± .04 
8. 2± . 04 
I3 ~H No. 4........ . 
Difference. 
.8 
■ i± • °S 7 
spotless parental families 
fNo 2<. 
• 4 
1. 2 
2. 3 ± • °9 
1. 9 ± .07 
1-3-12-14-2^ 5 . 
Difference... 
.8 
. 4 ± • 114 
. 2 
i 
•9 
1. 8± . 07 
2. i± .08 
3-2-4-I-22| No r 7 . 
Difference. 
• 7 
• 3± • 106 
There are, however, indications of a recombination of modifying 
factors in the hybrids. Evidence has been r presented that a slight degree 
of segregation took place in F 2 and it has been mentioned (p. 499) that in 
four pairs of F 3 progenies the means differed significantly, although each 
pair had the same 1? 1 grandparent. Nine of the 16 homozygous F s 
progenies, when compared with the population representing the respective 
dominant or recessive great grandparent (Table VIII) showed increase 
or diminution of the spot, the F 3 mean having differed from the parental 
mean by an amount equal to four or more times the probable error of the 
difference. The most pronounced of these differences are stated in Table 
XII, there being two cases in which dominant and three cases in which 
recessive F 3 progenies differed very significantly from the corresponding 
parental population. In one of the dominant F 3 ’s the spot was increased 
and in the other it was diminished. All three of the recessive F 3 ’s show a 
marked diminution of the spot, amounting in each case to a full grade. 
This evidence from F 3 can not be accepted without reservation, how¬ 
ever, for the reasons that soil heterogeneity of the plat used in 1923 
resulted in considerable differences in the rate of development and earli¬ 
ness of flowering of the plants in the various progenies and that the 
degree of expression of the spot appears to have been affected by the 
stage of development of the plant. 
The mean grade of petal spot was determined separately for the re¬ 
tarded and for the earlier-flowering plants in 11 recessive parental and 
F 3 progenies of 1923. In every progeny the more backward plants gave 
a higher mean grade than the more advanced plants, the average differ- 
