1:^6 Journal of Agricultural Research , ,l Voi. xxii, No. 3 



818, from Anderson, S. C, collected by R. O. Burns. 



918, from La Fayette, Ind., collected by E. H. Toole. 



3518, from Menah, Wis., collected by E. H. Toole. 



3818, from Wisconsin, collected by E. H. Toole. 



4518, from Superior, Wisconsin, collected by E. H. Toole. 

 Negative results were obtained on all but two species of the hosts used. 

 The collection from La Fayette, Ind. (No. 918), gave infection upon 

 Thalictrum angustifolium and T. aquilegijolium, producing, however, only 

 pycnia. It was impossible to carry this study further in 1919, as the 

 above results were not obtained until late in the spring. 



The failure of aecia to develop from the two successful infections could 

 be explained on either of two hypotheses. The conditions in the green- 

 house may have been unfavorable, or the species of Thalictrum used may 

 have been resistant. In either case, however, these results were inter- 

 preted as indicating that the aecial host of the leafrust of wheat was some 

 species of ThaHctrum. There was considerable basis for this assumption. 

 All of the culture studies being carried on in this laboratory with the 

 related rusts, occurring on wild grasses, and having aecia on members of 

 the family Ranunculaceae, have indicated that while a given race may 

 develop aecia on several species in one host genus with varying degrees 

 of virulence it will not go to species of more than one genus. The rusts 

 of this group show a very high degree of specialization. The two species 

 of Thalictrum on which infection was obtained were foreign species, 

 while the North American species, Thalictrum dioicum and T. polygarnum, 

 were not infected. On this account it was thought that the susceptible 

 aecial hosts for the leafrust of wheat probably were foreign species of 

 Thalictrum. As the leafrust of wheat presumably is an introduced form, 

 as explained in the following pages, this would be expected, and on that 

 basis the species of Thalictrum should be western Asiatic or eastern 

 European, corresponding to the region in which wheat is believed to have 



originated. 



CULTURES MADE IN 1920 



In preparation for cultural studies for the spring of 1920 an effort was 

 made during the summer and fall of 19 19 to obtain as many species of 

 Thalictrum as possible. It was impossible to obtain material from for- 

 eign botanical gardens in time to be of use, and the best that could be 

 done was to secure such species of Thalictrum as were carried by nursery- 

 men in this country, together with such native species as could be obtained 

 through collectors in various parts of the United States. As a result 14 

 species were brought together. An appeal was also made to the plant 

 pathologists in the various agricultural experiment stations tliroughout 

 the country for aid in securing telial material of the leafrust of wheat. 

 A very gratifying response to this appeal was made, and in this way 80 

 collections of telia were obtained and placed out to overwinter. Of 

 these, 51 collections germinated in the spring of 1920 and were sown. 

 The number of collections was so great that it was not possible to sow 



