58 



Journal of Agricultural Research 



Vol. xxn. No. a 



For total culm length, 6 of the ii varietal crosses showed an increase 

 over the parental average and 5 showed a decrease. The averages for 

 culm length of the F^ crosses and of their parents are practically identical 

 when the results of all crosses are considered together. This makes it 

 doubtful whether the increases of the F^ crosses over the parental averages 

 are the results of the vigor due to crossing or are due to some other 

 experimental factor. 



Table V. — Average yield of grain per plant of Fi wheat crosses and their parents 



For average yield of grain per plant, six of the eight variety crosses 

 yielded more than either parent, and all variety crosses jdelded more than 

 the parental average. Marquis X Bobs and Velvet Chaff X Little Club 

 exceeded the parental average 32 per cent in yield of grain per plant. 



With the exception of crosses between common wheat and Little Club 

 the average yield of grain per plant of the species crosses was less than 

 that of the lower-yielding parent. This is due to the fact that the F^ 

 plants had a high percentage of barren florets. 



STERILITY IN SPECIFIC CROSSES 



The occurrence of sterility in wheat specific crosses has been reported 

 by several workers. Tschermak {13), after several years of hybridiza- 

 tion work, found that hybrids of Triticum dicoccum and T. compactum or 

 vulgare varieties were only partially fertile. Hybrids of T. durum with 

 T. compactum or T. vulgare varieties were classed as fully fertile. Ster- 



