432 Journal of Agricultural Research voi. x, no. 9 



due to age, the rust was nevertheless often distinctly more virulent on 

 younger or older plants, depending on the peculiarity of the grass. 



The plants to be inoculated were moistened either with an at«mizer 

 or by rubbing water on with the fingers. The spores were applied with a 

 fiat inoculating needle in such a way as not to injure the leaves. After 

 inoculation the plants were placed in pans of water under thoroughly 

 cleaned bell jars, where they were left for 48 hours. They were then 

 removed and placed on ordinary greenhouse benches. During v/arm 

 weather, when it was necessary to keep the ventilators open much of 

 the time and there was some danger of contamination with wind-borne 

 spores, each strain was kept under a separate muslin cage such as those 

 under which the seedling plants were grown. A cage was not used again 

 for another strain of rust until first thoroughly disinfected with formal- 

 dehyde solution. 



All necessary precautions were taken to dispose properly of infected 

 material, and the greenhouse benches were drenched frequently with a 

 strong solution of copper sulphate in order to kill any spores which might 

 have fallen from the leaves. Accidental infections were almost entirely 

 avoided, as is shown by the fact that three different biologic forms were 

 kept more than two years, and many others were kept for shorter periods, 

 without any contamination whatever. 



Whenever there was any reason to suspect the presence of more than 

 one biologic form on a host as a result of inoculations with urediniospores 

 collected in the field, all available methods were used to isolate these 

 forms before drawing any conclusions. Further attention will be paid 

 to this in a discussion of the specific results obtained. 



The following varieties of cereals were used, except where otherwise 

 specified: Oats — Improved Ligowa, Minnesota No. 281 ; barley — ^Manchu- 

 ria, Minnesota No. 105; wheat — Bluestem, Minnesota No. 169; rye — 

 Swedish, Minnesota No. 2. Most of the grass seeds were obtained from 

 the Minnesota Seed Laboratory. A few were obtained from the Mon- 

 tana Seed Laboratory. The seed of the primitive barleys was fur- 

 nished by Dr. H. V. Harlan, of the Office of Cereal Investigations, United 

 States Department of Agriculture. 



RESULTS OF SURVEY 



The results of the inoculations made directly from the grasses collected 

 in the field are given in Tables I to XXVII. The direct inoculations 

 constitute only a small part of the work actually done. The various 

 rusts were often cultured in the greenhouse for varying lengths of time, 

 and as many inoculation experiments were made as seemed necessary 

 to establish the identity of the rust completely and to determine whether 

 it was in any way atypical. The results of these inoculations are given, 

 with the discussions of the various biologic forms. 



