526 Journal of Agricultural Research voi. xix, No. n 



(4) was always found associated with hairy chaff, and partial linkage 

 (jo) was found between the factors for black color and the factors for 

 glabrous chaflf. 



Since sterility has been found by many investigators in wheat crosses 

 and has been confirmed by the results presented in this paper, it seems 

 rather difficult to reach any conclusion regarding linkage, because some 

 combinations may be eliminated. 



The inheritance of the principal botanical characters of our cultivated 

 wheats is well known and, therefore, need not be summarized in this 

 paper. The inheritance of beards will be mentioned in connection with 

 our results on sterility. In crosses between the so-called beardless 

 wheats such as Marquis and Bluestemand a bearded variety, the F^ gen- 

 eration has intermediate awns and in the F2 generation a i to 2 to i ratio 

 is obtained. Fully bearded plants breed true in the F3 generation. How- 

 ard and Howard {14) found that there are two classes of wheats with 

 short awns which, when crossed, give fully bearded plants in the F^ gen- 

 eration and breed true in the F3 generation. Likewise, crosses between 

 bearded and true beardless forms gave i fully bearded plant in the Fg 

 generation out of 16 plants. The fact of interest for our studies is that 

 fully bearded plants breed true for this character. 



PREVIOUS STUDIES ON INHERITANCE OF RUST RESISTANCE 



The most successful attempt to breed rust-resistant wheats was made 

 by BifFen (2, j, 5), who found that resistance to striperust {Puccinia 

 glumarum Enkss. and Henn.) was a recessive character. Definite 

 segregation occurred in the F2 generation, and forms bred true in the F3 

 generation, the ratio of resistant to susceptible in the segregating families 

 being i to 3. From the practical standpoint these experiments have been 

 very valuable. A new variety, Little Joss, was produced, which, because 

 of its rust resistance, yields more on the average than susceptible sorts 

 and has desirable milling characters. 



Nilsson-Ehle (20) has likewise made studies of the inheritance of 

 resistance to striperust. Distinct dominance of susceptibility was seldom 

 found. Ordinarily the F^ generation was intermediate, and in other cases 

 resemblance to one or the other parent was observed. Segregation was 

 obtained in the Fj generation, but without definite ratios. Transgressive 

 segregation occurred, forms being obtained which were more susceptible 

 than the susceptible parent and others which were more resistant than 

 the resistant parent. The results were explained on the basis of multiple 

 factors. 



While many observations have been made on resistance of wheat 

 varieties, the two experiments cited above are the only carefully con- 

 trolled studies so far reported which show the mode of inheritance. 



