346 
Journal of Agricultural Research 
Vol. XXIX, No. 7 
DISCUSSION 
EARLINESS IN THE Fi GENERATION 
According to the investigations re¬ 
viewed earlier in this paper, in two cases 
(6, 3) the time of maturity in wheat 
crosses was intermediate in the Fi, while 
in two others (2, 15) it was inclined to 
the late parent. In experiments with 
oats W), corn (5), and cotton (13), the 
time of maturity was found to be inter¬ 
mediate; in rice (10) it was intermediate 
but inclined to the early parent; in ex¬ 
periments with peas it was found to be 
intermediate in one (1), while in the 
other (10) it was inclined toward the 
late parent. The exact behavior in the 
Fi was not recorded in the Marquis X 
Sunset cross reported in this paper. It 
is very probable that time of maturity 
is intermediate and possibly inclined 
toward the early parent, as behavior in 
the F 2 and F 3 shows earliness to be 
dominant. 
EARLINESS IN THE F 2 GENERATION 
The curve of the data for the F 2 , as 
shown by Figure 3, indicates strongly 
the presence of one main allelomorphic 
pair of factors for earliness in this cross, 
as there is a distinct segregation of the 
population into a large early group and 
a small late group in a ratio of nearly 
3:1 (3.07:0.93). The modes of the 
two groups diverge from those of the 
parent varieties toward the intermediate 
position, which would indicate the 
presence of modifying factors also. 
The class of greatest frequency of the 
early group is only two days later than 
that of the early parent, whereas in the 
late group it is five days earlier than that 
of the late parent. 
EARLINESS IN THE F 3 GENERATION 
If the inheritance of earliness in this 
cross can be explained by a single pair 
of factors, the recessive late group 
should breed true in the F 3 . Nearly 93 
per cent of the recessive late individ¬ 
uals from the F 2 were late in the F 3 
and, considering the total population, 
the ratio of early to late was 3.09 to 
0.91, which indicates that a one-factor 
hypothesis for this cross is correct. 
Further evidence in favor of this view 
is furnished by the fact that over one- 
half of the F 3 rows were homozygous 
for earliness, as shown by the time- 
temperature unit method of analysis 
according to segregation in the F 2 , 
AA+2Aa+aa. 
This experiment is subject to a cer¬ 
tain amount of error from various 
sources. Late or premature heading 
may be caused by variation in the 
amount of available soil nutrients, poor 
drainage, disease, mechanical injury, 
etc., but with considerable numbers 
these factors should have little or no 
effect on results. The index for the 
end of the heading period is less defi¬ 
nite and more difficult to obtain where 
material is not sacrificed, as was the 
case in this experiment. Some diffi¬ 
culty was encountered in connection 
with second-growth culms or tillers 
which appeared in the late segregates 
after the spring rains, but these were 
quite successfully disposed of by ignor¬ 
ing such culms below the knee in height. 
Close examination was also necessary 
on account of the large number of 
culms in each row, yet it is believed 
that fairly accurate data were procured 
in this study. 
SUMMARY 
The cross Sunset X Marquis and its 
reciprocal were used in this study. 
The Sunset parent, an Australian 
variety, is one of the earliest wheats 
known. The Marquis parent, the 
well-known hard spring wheat grown 
in Canada and the northern United 
States, is a midseason to late variety 
in California. 
The cross was made at Chico, Calif., 
in 1920. The Fi was grown at Chico 
in 1921, and the F 2 and F 3 generations 
at Davis, Calif., in 1922 and 1923. 
The inheritance of time of maturity 
in wheat and other plants has been 
studied by a number of investigators. 
The Fi has been found to be interme¬ 
diate or inclined to one or the other 
parent. In the F 2 there has been a 
tendency for the intermediate condition 
to be maintained with a range of 
variation almost covering the extremes 
of the parents and both with and 
without the grouping into classes 
showing definite segregation. 
It is believed that the best index in 
a study of earliness and lateness in 
wheat is the date of appearance of the 
tip of the first spike on the plant. 
Slight differences are more magnified 
at this time than at the period of 
ripening. 
No data were secured on the Fi 
generation. Other investigators have 
shown that time of maturity in wheat 
is either intermediate or inclined to 
the late parent in this generation. 
In the F 2 there was a distinct heaping 
up of the population into a large early 
and a small late group in the proportion 
of 3.07 to 0.93, indicating one allelo¬ 
morphic pair of factors, with possibly 
a number of minor modifying factors. 
