34 THE RUSTS OF GRAINS IN THE UNITED STATES. 



were carried without a break until August, 1909. In these experi- 

 ments 52 generations of uredospores were grown without the inter- 

 vention of any other spore form. These generations consisted of 

 Puccinia graminis on wheat, barley, and oats; P. ruhigo-vera on wheat 

 and rye; P. simplex on barley; P. graminis, originally from barley, 

 on wheat; and P. graminis, originally from wheat, on barley. At 

 the end of these experiments cultures were as easily made and the 

 rusts grew as luxuriantly as at the first inoculation with material 

 obtained directly from the field. 



In these experiments care was taken to avoid accidental infection 

 from outside sources. Plants showing indications of such infection 

 were destroyed. As far as possible series of 10 plants were used and 

 each inoculation was made with material from separate leaves of the 

 stock plants. The source plants were always maintained until evi- 

 dence of successful infection appeared. If infection did not take 

 place by reason of unfavorable conditions at the time of inoculation, 

 inoculations were again made from the source plants. For instance, 

 if A was used to inoculate B, A was not destroyed until B showed 

 fresh pustules. If B gave no evidence of the presence of rust, another 

 B was inoculated from A. The following rusts were used: Puccinia 

 graminis on wheat, P. graminis on oats, P. graminis on barley, P. 

 graminis on rye, P. rubigo-vera on wheat, P. simplex on barley, P. 

 coronata on oats, and P. ruhigo-vera on rye. 



The original source material was brought from the ^Minnesota Agri- 

 cultural Experiment Station, October 5, 1906. Between that date 

 and February 6, 1907, at least four transfers were made, probably 

 as many as six or eight. During a part of the time the series were 

 run at Alinnesota and the remainder of the time at Wasliington, D. C. 

 When transfers were to be made, heavily pustuled leaves were picked, , 

 inclosed in envelopes, and sent by mail. Inoculations were made on 

 their arrival at their destination. Infection almost invariably took 

 place readily. The transfers were necessary by reason of change of 

 location of the men in charge of the experiments. 



SUMMARIES OP THE EXPERIMENTS. 



The following tables give the dates when all inoculations were made 

 as well as the number of successful infections from each inoculation: 



216 



