524 Journal of Agricultural Research voi. xxx. No. n 



virulence of the rust, is probably incorrect. More recent investigations 

 of the wheatrust fungus have shown that there are numerous biologic 

 forms (25) which can be differentiated only by their action on various 

 pure-line wheat varieties. This is a very serious obstacle to the produc- 

 tion of rust- resistant varieties by breeding, although the fact that Khapli 

 (C I 4013),^ an emmer imported from India, is resistant to all biologic 

 forms so far isolated shows that the problem is not entirely hopeless. 



Former breeding investigations have determined which varieties of 

 wheat are commonly resistant to stemrust at University Farm, St. Paul, 

 and have also indicated the behavior of rust resistance in crosses. In the 

 light of this information it was decided to make a careful genetic study 

 of one or two crosses, hoping thus to solve the plant-breeding phase of 

 the rust-resistance problem. The second generation of the crosses 

 reported in this paper had already been studied before it was known that 

 there were sometimes numerous biologic forms of the rust in the same 

 locality. It seemed worth while to complete the study of inheritance of 

 rust resistance in these crosses by growing a small F3 family of each Fj 

 plant which produced viable seed. All barberry bushes were removed 

 from the immediate vicinity of the rust plot early in the spring of 1918, 

 and the artificially induced epidemic was produced with a known racial 

 strain of the biologic form Puccinia graminis tritici Erikss. and Henn. 

 Therefore, the greater part, if not all, of the rust infection present during 

 the season of 191 8 was due to this one biologic form. One uredinium 

 found on Kanred (C I 5146), which is known to be resistant to the strain 

 which was used to induce the epidemic, proved to belong to another 

 biologic form. 



The present paper is a report of the inheritance of rust resistance in its 

 correlation with botanical and morphological characters of crosses 

 between Triticiwi vulgare with varieties of T. durum and T. dicoccum. 



SOME PREVIOUS CROSSES OF WHEAT SPECIES 



Because of the many differential characters and the great economic 

 importance of the crop, wheat has been frequently used in studies of the 

 laws of inheritance. Vilmorin {26, 27) reported quite extensive tests of 

 crosses between Triticum sativum T-, T. turgidum, T. durum, Desf., 

 T. polonicum T-, and T. spelta. From the Mendelian standpoint the 

 results obtained are interesting. He observed remarkable uniformity 

 in the F^ generation, wide diversity in the Fj generation, and states 

 that the predominating force after the F3 generation is that of heredity, 

 which compels the plants to reproduce their characters in their immedi- 

 ate descendants. Vilmorin placed spelt and common wheats in one group 

 and poulard and durum in another, because he found that either spelt 

 or common crossed with poulard or durum produced all four types in the 



1 Cereal investigations number. 



