22 
BULLETIN" 1403, U. S. DEPARTMENT OF AGRICULTURE 
In 1924 at Bozeman, Moccasin, and Havre F 3 strains were grown 
in nursery rows with one or the other of the two parents as a check 
every tenth row. Three notes were taken on dates of heading at 
each point: (1) First heading, (2) 50 per cent headed, and (3) fully 
headed. A careful study of all these data indicates that first heading 
is the most definite and therefore the niost valuable of the three notes. 
The frequency data obtained on first heading are shown for the three 
stations in Table 22 and graphically in Figure 2. 
The data in Table 22 give further evidence that early heading is 
partially dominant, the mean date of first heading of the hybrids at 
the three stations averaging 2.5 days later than the early parent and 
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Fig. 2. — Frequency distribution of F3 hybrid wheat strains and the range of variation of the 
Marquis and Hard Federation parents, together with their average dates of first heading at 
Bozeman, Moccasin, and Havre, Mont., in 1924 
3.3 days earlier than the later parent. The F 3 data for date of first 
heading on a row basis show greater variability for the F 3 hybrids 
in comparison with the parents than did those for date of heading 
of individual F 2 plants. 
At Bozeman 25 F 3 strains and at Havre 16 of the same strains 
were studied in 1924 on an individual-plant basis by labeling the F 3 
plants for date of heading. Duplicate rows of each of the parent 
varieties were studied in a similar manner. There were some marked 
variations among the frequency distributions of the various F 3 
strains, in that some approximated smooth curves and others bimodal 
curves. Strain A3-90 in Table 23 is an example of a bimodal curve. 
