466 
Journal of Agricultural Research 
Vol. XXIV, No. t 
With this fact established, it has been possible to inoculate the progeny 
from this cross with a single biologic form of rust from which the Kanred 
parent is immune. By their reaction to this one form it is clear that 
without inoculating they will react similarly to the other biologic forms 
from which Kanred is immune. In this manner, numerous Fg selections 
have been obtained which are pure spring types immune from all of the 
known biologic forms of stem rust from which the Kanred parent is 
immune. 
DISCUSSION OF results 
The results show very clearly the complicated nature of the genetic 
difference between a spring and a winter variety of wheat. The results 
could not be explained very well on a simple monohybrid or dihybrid 
basis. The segregation indicates very minute differences for this char¬ 
acter between the individual plants. While the time of heading was 
divided only into weekly periods, it was very evident during the progress 
of the experiments that the differences between the individual plants 
could be determined within a few days. For practical purposes and 
convenience in gathering the data, however, it was decided that heading 
periods, one week in duration, would be sufficient to indicate accurately 
the nature of the segregation for this character. 
The results presented in Table IV show that there was no correlation 
between the growth-habit character and reaction to rust. The same 
numeric relations exist between the susceptible and resistant plants 
regardless of their respective times of heading. This transfer of the 
rust resistance of thd* winter parent to the progeny having the growth- 
habit character of the spring parent, attained the initial objective of the 
experiment. Several thousand rust-resistant families were obtained in 
the Fg and F4 which are being studied and tested for desirable agronomic 
characters in general. 
These results are of particular interest not only in that they contribute 
to the solution of the general problem of breeding varieties of wheat 
resistant to rust, but also from the biological viewpoint. It is a common 
opinion that winter forms are more ancient or primitive than spring forms. 
Vavilov points out that this opinion is based on the fact that the so-called 
wild progenitors of our cereals are winter forms. Upon closer investiga¬ 
tion of these wild species, however, he discovered the existence of spring 
as well as winter forms. He states {18): 
As a matter of fact, spring races in natural conditions have originated as a result 
of hybridization of different varieties of winter plants, and, vice versa, spring varieties 
could give origin to winter varieties. Both kinds of plants can be obtained sjmtheti- 
cally one from another. 
The wide genetic variability which different varieties of wheat may have 
for growth habit explains why spring character may be dominant over 
winter character and vice versa. The segregation which one would expect 
in a cross depends upon the factors present for the growth-habit character 
in the parental material. One might cross two varieties of winter wheat 
which from all appearances seemed to be homozygous for winter habit 
and in the progeny obtain some plants with the spring habit of growth. 
It has been shown {18) that spring types have appeared in the Fg of 
such a cross. Likewise two spring types may 1 ^ crossed and some 
progenies which are winter t)pes will be obtained. This has been 
shown (5) in the case of two varieties of spring barley, in the Fg and F^ 
of which appeared several winter forms. 
