26 
BULLETIN 1403, IT. S. DEPABTMEXT OE AGEICTJLTTJEE 
RIPENING PERIOD 
In inheritance studies of maturity in several crosses Thompson 
(19) found that the date of ripening in the F x generation was near 
that of the mean of the later parent. In the F 2 generation most of 
the plants were intermediate between the parents, indicating blending. 
The apparent dominance of late ripening in the F x generation was 
explained as due to heterosis, and the further results on ''the multiple 
determiner hypothesis of blending.'' 
The plan of the present study was to determine the inheritance of 
earliness as measured both by date of heading and date of ripening, 
and also the importance of the intervening fruiting period. Xo com- 
parison of the dates of ripening of the F t hybrids with those of the 
parents are available, but F 2 data are available from different 
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Fig. 3. — Frequency distribution of Fa and F3 hybrid wheat plants and the range of variation of 
the Marquis and Hard Federation parents, together with their average dates of ripening at 
Bozeman, Mont., in 1923 and 1924 
families of reciprocal crosses grown at Bozeman and Moccasin in 1923. 
Unfortunately, the parent varieties were not grown at Moccasin. 
The date of ripening was recorded when the last green color dis- 
appeared in the peduncle and the kernels were firm to the pinch of the 
thumb-nail. Kernels in the different heads of some plants varied 
from dead ripe to soft dough. For this reason maturity was deter- 
mined by the average ripeness of the stems and kernels combined. 
The plants were harvested daily, and the date of ripening was recorded 
on the envelope in which heads from individual plants were placed. 
The data obtained in the F 2 generation are presented in Table 27 
and the Bozeman data shown graphically in Figure 3. 
The Bozeman data in Table 27 and Figure 3 indicate dominance 
of early ripening as the hybrids average less than 2 days later than 
