VARIABILITY IN LINKAGE OF CHARACTERS OF MAIZE 35 
It should be noted also that in this hybrid the crossing over is 
lower in the female. It agrees in this respect with the second 
progeny of Dh 416 and suggests the idea that the effect of heterozy- 
gous R may be apparent only when the crossing over is low. 
It is obvious that the effect of heterozygous R is influenced by the 
nature of the gametic composition and that the apparent differences 
are reduced by combining all classes, as has been done in Table 22. 
With the present data, however, it seems unwise to go farther than 
to conclude that heterozygous R is associated with a reduced crossing- 
over. 
Additional evidence is to be found in the published data of Kemp- 
ton (11 pp. 71-73). His tables give the correlation between and 
Wx in two groups of ears, one homozygous for R and the other with 
R heterozygous. The R R group has 20 ears with 12,394 seeds and 
a mean crossing over of 24.9 ±0.33 per cent. The R r group has 4 
ears with 2,477 seeds and a mean crossing over of 23.3 ±0.40 per 
cent. The difference is 1.6±0.52 per cent, a little more than three 
times its probable error. 
RATE OF CROSSING OVER BETWEEN C AND Wx ASSOCIATED WITH THE Su FACTOR 
In view of the fact that the rate of crossing over between C and 
Wx is reduced when the aleurone factor (R) not in the chromosome 
with the linked pair is in a heterozygous condition, it becomes of 
interest to test the effect of other factors not involved in the produc- 
tion of color. 
Material was available involving the factor for sweet endosperm Su. 
The hybrid furnishing this material had as one parent a strain of 
the Dh 416 cross used throughout the present study, but the parent 
providing the sweet endosperm was from an entirely unrelated 
variety. The Dh 416 parent with respect to the factors under dis- 
cussion was constituted C R R wx wx Su Su, and the sweet parent 
had the gametic constitution of cc rr WxWx susu. 
Crossed seed was colored horny, and the F x plants when self-polli- 
nated had colored and white seeds in the ratio of 9 to 7. With 
respect to the texture of the endosperm the seeds were classed as 9 
horny, 3 sweet, 3 waxy, and 1 waxy-sweet. Colored-horny and white- 
waxy seeds were planted and back-crosses obtained between them 
after the homozygous horny plants had been eliminated by means 
of pollen tests. 
The complicated aleurone and endosperm condition necessitates 
-subdividing the data to differentiate the several types of ratios, and 
the data are considered further from the standpoint of sex. 
The ears composing these several groups are found in Table 23. 
.Since the primary consideration is to test the effect of heterozygous 
.Su as compared with homozygous Su, each aleurone group is divided 
into two classes on the basis of whether or not sweet seeds were 
produced. Since all the ears tested are the result of back crosses on 
white-waxy plants that were either heterozygous or homozygous for 
.Su, it is not possible to identify the ears in the nonsweet group that 
were lieterozygous for Su in one parent but were fertilized with 
pollen from a plant homozygous for Su. A certain proportion of 
the ears having no sweet seeds in one parent or the other, therefore, 
were heterozygous for Su. With this limitation in mind, the tables 
