BLACK STEM RUST Ol^^ WHEAT. 57 



be considered as established hosts for the black stem rust of wheat in 

 thiscountry: THticumvaUfare, T. compact urn, T.turgichim, T.<luru)n,a,ml 

 Hordeum vulgare — cultivated varieties, and T. monococeuni, T. poloni- 

 cum, and H. juhaium. 



It is almost certain that the following species also act as hosts for 

 this rust form: Triticum. spcHa and T. dicnccum — cultivated varieties, 

 and Agropyron richardsotU, A. tenerum, Elymus canadeims, and E, cana- 

 densis glaucifolius. 



Occurrence and distrihution. — As to the occurrence of this rust in the 

 United States, little need be added to what has already been said. A 

 fact of i)articular importance is that the stem rust, unlike the leaf rust, 

 is not constant in occurrence, but will occasionally miss one or two 

 years in five or six, depending, however, pretty much upon the locality. 

 Although sometimes very destructive in any part of the United States 

 except the irrigated districts, it probably produces serious damage 

 most frequently in the Central States, between Xew York and Missouri, 

 and in certain portions of Texas and California. In foreign countries 

 this rust is especially common in northern Europe, and in certain sea- 

 sons it is (]uite abundant also in Australia and Tasmania. According 

 to Barclay (5, Vol. XXX, pp. 45-47), it is com])aratively unimportant 

 in India. 



Wintering of the uredo. — Australia is the only country in which it has 

 been demonstrated that the uredo winters over. Here, accoiding to 

 Cobb (19, p. 29), P. graminis lives the entire year in the uredo stage, 

 either on self-sown grain or on certain native grasses, but whether he 

 refers to one or to both of the forms of the rust on wheat and oats is 

 not known. The writer has made a number of investigations to deter- 

 mine the question for this country, giving considerable time to the 

 matter each winter, but has not yet been able to trace uredospores 

 through the winter, although the form on oats has been found to live 

 much longer than that on wheat. 



Failing to find that the uredo winters over in Kansas, the writer 

 thought that it might do so farther south, where the winters are milder, 

 and that as spring advances the uredospores would be wafted north- 

 ward from field to field and produce infection in their line of progress. 

 In the hope of settling this point, therefore, he made a two-weeks' 

 tour in December,1895, through the State of Texas, from Indian Terri- 

 tory to the Mexican line. All the small grains except barley were 

 closely examined in numerous fields around Fort Worth, Austin, Laredo, 

 Houston, Beaumont, College Station, and McKinney, but it was rather 

 surprising to find not only no trace of Uredo graminis either on wheat 

 or winter oats, but also no Uredo ruhigo-vera on wheat or rye. Winter 

 oats was seen growing as far south as Laredo, but no trace of rust or 

 of any other fungus could be found on any of the plants, although in 

 examining old straw at several different places plenty of evidence was 

 found that all the rusts of wheat and of oats were present during the 

 preceding summer. 



