June 15, 1920 Relation of Rust in Seed Wheat to Seedling Infection 259 



rence of Euphorbia rust (Uromyces euphorbiae C. and P.) upon seeds of 

 Euphorbia dentaia. Various writers have noted P. malvacearum Mont. 

 on hollyhock seeds. Otlier examples of a similar nature could be given. 

 The discussion of the practical importance of this occurrence in relation 

 to subsequent infection of seedlings will be taken up in a later paragraph. 



ABUNDANCE OF KERNEL INFECTION IN WHEAT 



In order to learn to what extent seed wheat may become infected with 

 Puccinia graminis tritici a large number of wheat samples were ex- 

 amined by the writer. These samples were secured from various sources 

 and from the crops of the two years 1915 and 191 6. During the fall and 

 winter of 1915-16 samples of wheat were secured from various points in 

 North and South Dakota, from western Minnesota, from grain commis- 

 sion firms in Minneapolis, and from wheat grown in the rust nursery at 

 the University Farm, St. Paul, Minn. In all, several hundred samples 

 of wheat were examined, all of which came from fields known to be badly 

 rusted or from localities where it was known that rust epidemics had 

 occurred. During the fall of 191 6 a large number of samples of wheat 

 were obtained from the same regions as in the previous year. In those 

 regions there occurred that year an unusually severe rust epidemic. It 

 would seem, therefore, that under these conditions there would be as 

 large an amount of seed infection as ever occurs. 



It was found at once that the task of determining the percentage of 

 infection was not so easy as it at first appeared. In some cases the 

 kernels were found to be but slightly infected, having only one sorus on 

 the hilum, or germ end. In such cases it was impossible to see that 

 these were infected at all except by means of examination under con- 

 siderable magnification. In other cases the general appearance of the 

 kernels seemed to indicate to the unaided eye that there was rust infection, 

 but upon examination under the microscope no rust was found. Indica- 

 tions were that such discolorations were caused by some other agency. 

 Altemaria and Helminthosporium species were often found to be asso- 

 ciated. In general, it was found impossible to tell in every case whether 

 or not a kernel was infected by rust except by microscopic examination. 

 However, in many cases, especially after some experience, many of the 

 rust-infected kernels could be easily detected by the unaided eye. 



The large majority of the rust-infected kernels, when mature, were 

 found to bear only telia,^ which appeared as gUstening black specks on 

 the hilum, or the germ end, or a short distance down the groove of the 

 kernel. Sometimes sori were noted a short distance from the hilum with 

 no surface connections between these and the ones at the hilum (see PI. 

 39, B). Upon sectioning similar kernels, however, the mycelial connec- 

 tions were found. If the hilar end of an infected kernel is scraped with 

 a sharp knife or scalpel, teliospores in abundance can be secured. 



' Uredinia were noted on immature kernels at various times. 



