May 12,1923 
Resistance to Stem Rust in a Cross of Common Wheat 463 
The plants selected from the first heading period in the second generation 
were homozygous for the spring habit of growth in the third generation. 
Beginning with the plants in the second heading period, there was a 
gradual decrease in the number of families which were homozygous for 
the spring character and a corresponding increase in the number of 
families heterozygous for the same character as the seventh heading 
period was approached. There was also a gradual change in the ratios 
of spring to winter types progressing from the first to the seventh heading 
period. In the seventh period, 2 families were homozygous for winter 
character. If the plants in the eighth class had produced seed in the 
second generation, there undoubtedly would have been a still larger 
number of homozygous winter types in proportion to the number of 
spring types. 
One can readily see from the data presented that there is a great 
difference in degree of heterozygosity of the plants in the various heading 
periods. In the first heading period all 10 of the Fg families are homo¬ 
zygous for spring type; in the second, 6 of 10; in the third, 7 of 10; in the 
fourth, 5 of 10; in the fifth, 2 of 10; in the sixth, all 9 of the families are 
heterozygous for growth habit, and in the seventh period 4 families are 
heterozygous for growth habit and 2 are homozygous for winter type. 
With the exception of those from the sixth heading period, homozygous 
forms were obtained in all classes grown. A number of Fg families were 
homozygous spring types comparable to our ordinary hard red spring 
wheat varieties. In addition to these early-heading plants, a few families 
were obtained which were homozygous for a heading period much later 
than that of the Marquis parent. 
From Table III it will be noted that there is a correlation between the 
Fg heading period and the percentage of spring types produced by the 
various Fg families. 
Tabi,]^ III .—Showing the growth habit of the F^from Fg plants heterozygotis for growth 
habit 
Heading period. 
Number of types. 
Spring 
types. 
Spring. 
Winter. 
I... 
All. 
154 
121 
158 
236 
187 
12 
None. 
14 
39 
46 
69 
6 
Per cent. 
100 
92.2 
89.6 
80.2 
83.7 
73 
66.7 
2 . 
A . 
e. 
6 . ' .. 
7. 
With the exception of the very slight increase in the fifth heading 
period, there is a very regular decrease in the percentage of spring types 
to winter types as one proceeds from the first to the seventh heading 
period. Here also there undoubtedly would have been a more complete 
reversal of the ratios of spring t3rpes to winter types in plants of the 
eighth and ninth heading periods, had it been possible to grow these plants 
in the third generation. 
