June 7 ,1924 A Genetic and Cytological Study of Wheat Hybrids 1025 
number of grains per spikelet. Segregates resembling the Alaska parent are the 
most fertile, followed by those resembling the vulgare parent. The intermediate 
types which could be placed in no particular group were the most nearly sterile • 
Table IV.— Segregation and average fertility of various types of Fz segregates in 
Marquis X Alaska 
Type head 
Number 
Grains per 
spikelet 
1 . Vulgare......... 
426 
1.43 
3. Spelta............. 
155 
1.18 
4. Durum........... 
307 
1.23 
5. Turgidum...... 
49 
1.70 
6 . Emmer......... 
154 
1.33 
9. Abnormal....... 
429 
.81 
The various types of segregates obtained in the F 2 of Marquis X Alaska and 
in the cross Hybrid 143 X Polish are shown in Plate 1. In the first case segregates 
are obtained which resemble either parent and also individuals which resemble 
T. spelta and T . durum . Types resembling T . compactum were also obtained 
but these may be due to mixtures. In the second cross types similar to T. * 
durum were obtained as well as a number of types unlike any cultivated species. 
The segregates with very long glumes but with short heads as shown in Plate 1, 
C, b were found to be quite sterile in most cases. 
THE ASSOCIATION OF VARIOUS CHARACTERS IN SPECIES HYBRIDS 
It has been pointed out that in the more sterile hybrids the intermediate types 
would be more rapidly eliminated and the surviving segregates in F 2 and F 3 
might resemble the parental types more or less closely. In more fertile crosses, 
on the other hand, the intermediate types might survive for several generations 
and gradually become eliminated only after a number of years. Since certain 
characters are found only in the emmer wheats and other characters are found 
only in the vulgare wheats one might expect a higher degree of association of 
these characters in F 2 segregates of relatively sterile hybrids, while there would 
be comparatively little association of parental characters in the more fertile F 2 
segregates due to the fact that the intermediate types are not so rapidly elimi¬ 
nated. Thus, for instance, in one cross the F 2 and F 3 segregates consist largely 
of individuals with approximately 14 or 21 chromosomes, and there would be 
little opportunity for combinations to occur possessing characteristics of both 
parental groups. If, on the other hand, the cross resulted in an F 2 progeny which 
was relatively fertile and included many types with an intermediate chromosome 
number, then there would be more or less combination of parental characters 
and less association between the characters peculiar to each group. 
96461—24t-4 
