June 7, 1924 A Genetic and Gytological Study of Wheat Hybrids 1031 
bine the drought and disease resistance of the emmer species with the high quality 
of the vulgare wheats without successful results. 
In general, the intermediate types of segregates are more sterile than segregates 
resembling one parent or the other (Tables IV and V). Individuals resembling 
one economic species of wheat are more fertile than those which can not be so 
classed. 
There is a greater proportion of intermediate types in the more fertile species 
hybrids, which may indicate that more of the segregates can function with an 
intermediate chromosome number in such crosses. A cytological examination 
of F 4 segregates shows that the intermediate types usually have an intermediate 
chromosome number but some of the segregates with 14 and 21 chromosomes also 
possess characteristics of both parents. The presence of some of the typical 
vulgare characters in 14 chromosome segregates and the occasional recovery 
of emmer characters in 21 chromosome segregates suggest that the chromosomes 
which carry the factors for the distinguishing vulgare characters may in some 
cases at least pair with certain of the emmer chromosomes in crosses between 
members of the two groups. The combinations of typical emmer and vulgare 
characters in certain segregates indicates that the differentiating vulgare char¬ 
acters are determined by factors in individual chromosomes and not by the 
combined effect of the additional seven chromosomes. 
Although in the more fertile crosses there are many segregates with interme¬ 
diate chromosome numbers it is questionable if such segregates can persist in a 
homozygous fertile condition. Certain combinations of emmer and vulgare 
characters do occur in segregates with 14 or 21 chromosomes and it is probable 
that a small proportion of segregates can be obtained which will combine certain 
characters of the two groups of species, especially in the more fertile combina¬ 
tions. From a practical standpoint, however, it would probably be more feasible 
to combine disease resistance and yield and quality of grain by selecting the 
parents within the vulgare group. It is perhaps significant that crosses or 
vulgare varieties are apparently the only ones which have resulted in new varieties 
of economic importance. 
LITERATURE CITED 
(1) Belling, J. 
1921. ON COUNTING CHROMOSOMES IN POLLEN-MOTHER CELLS. Amer. 
Nat. 55: 573-574. 
(2) Biffen, R. H. 
1912. STUDIES IN THE INHERITANCE OF DISEASE RESISTANCE. II. Jour. 
Agr. Sci. 4: 421-429. 
(3) Clark, J. A., Martin, J. H., and Ball, C. R. 
1922. CLASSIFICATION OF AMERICAN WHEATS. U. S. Dept. Agr. Bui. 
1074, 238 p., illus. 
(4) Gaines, E. F. 
1917. INHERITANCE IN WHEAT, BARLEY, AND OAT HYBRIDS. Wash. Agr. 
Exp. Sta. Bui. 135, 61 p., illus. 
( 5 ) - 
1920. THE INHERITANCE OF RESISTANCE TO BUNT OR STINKING SMUT OF 
wheat. Jour. Amer. Soc. Agron. 12: 124-132. 
(6) Hayes, H. K., Parker, J. H., and Kurtzweil, C. 
1920. GENETICS OF RUST RESISTANCE IN CROSSES OF VARIETIES OF TRITI- 
CUM VULGARE WITH VARIETIES OF T. DURUM AND T. DICOCCUM. 
Jour. Agr. Research 19: 523-542. 
