158 THE ROYAL SOCIETY OF CANADA 



University, in his breeding experiments, had suggested very strongly 

 that such strains did exist. 



The task of the Canadian plant pathologist, then, is to gain a 

 definite knowledge of the number, characteristics, and geographical 

 distribution of the biologic forms in Canada. It was with this end in 

 view that this investigation was undertaken. Three years' results 

 are now available and are presented in the following pages. It is 

 hoped that they may be of immediate practical assistance to plant 

 breeders. 



Experimental Materials and Methods 



Collections of rust were made in the field from the time the first 

 pustules appeared in early summer until late in September. It was 

 thought that if the observation were correct, that rust moves north- 

 ward in waves across the continent, then possibly different biologic 

 forms of rust might appear at different periods of the summer. 



Material was collected in 81 representative localities of Manitoba, 

 Saskatchewan and Alberta. 



All the preliminary work of differentiating the numerous rust 

 collections into distinct forms was carried out in the greenhouse, where 

 conditions could be more definitely controlled than in the field. 



Differential Hosts 



The identification of the biologic forms necessarily involved the 

 use of many varieties of wheat as differential hosts. Preliminary 

 experiments with a number of different groups of wheat varieties 

 indicated that the series used for this purpose by Stakman and his 

 co-workers at the University of Minnesota were by far the most 

 satisfactory. The list which this series comprises is given in Table I. 

 The name of the variety is preceded in each case by the abbreviation 

 used in the key and in the tables presented later. 



Table I. — List of differential hosts used in identifying biologic forms. 

 Triticum aestivum 



KRd— Kanred, C. I. 5146 (Kans. 2401). 



Ko— Kota, C. I. 5878. 



Ma— Marquis, C. I. 3641 (Minn. 1239). 

 Triticum compactum 



Lc— Little Club, C. I. 4066. 

 Triticum dicoccum 



Em— Emmer, C. I. 3686 (Minn. 1165). 



Kpl— Khapli, C. I. 4013. 



