196 THE ROYAL SOCIETY OF CANADA 



ceptibility and resistance of individual F2 plants to the two biologic 

 forms appeared. Out of a total of 388 plants 35 were highly resistant 

 to both forms of rust. This makes it reasonable to assume that 

 varieties resistant to more than two biologic forms may be produced 

 by hybridization." 



In conclusion, attention is directed to the fact revealed in Table 

 III that genetic material bearing the necessary factors for rust resis- 

 tance is available in the common and durum wheats (without having 

 recourse to the difficultly hybridizable einkorn and emmer) for 11 of 

 the biologic forms isolated in Canada. Of the remaining 3 forms one 

 is of rare occurrence, and the other two are of not more than moderate 

 frequency. It will be seen that Kanred, a variety of winter wheat, 

 is completely immune to all 6 forms of the important predominating 

 group discussed above. Thus, the required tools are at hand. The 

 task is by no means impossible of accomplishment. For the patient 

 and painstaking labour of the plant breeder it promises rich reward. 



Summary of Part I 



1. Fourteen biologic forms of Puccinia graminis tritici have been 

 demonstrated by infection experiments to be present in Canada. 



2. All of these forms, as well as some others, are found in the 

 United States. 



3. Strain XVII was always the first form to appear each season, 

 and IX one of the last forms to be collected. This suggests that the 

 former may be more local in origin and the latter carried by winds 

 from farther south. 



4. The geographical limits of the forms isolated have been 

 tentatively mapped, but will, no doubt, be extended by further 

 exploration. 



5. A rather virulent form, XVII, was found to be quite widely 

 distributed, being collected in twenty-six different localities of Mani- 

 toba, Saskatchewan and Alberta. 



6. Preliminary infection experiments with 29 species of grasses 

 are reported. 



7. As Stakman has pointed out, "Methods of breeding for rust 

 resistance must now be changed fundamentally. The breeder must 

 know and work with those forms of rust which occur in the region 

 for which his new variety is intended." 



8. The six forms, I, IX, XVII, XXI, XXIX, XXX, all of which 

 give the same reactions on the bread wheats, constitute 70 per cent, 

 of all the collections. Thus the production of a spring wheat variety 



