18 



INVESTIGATIONS OF RUSTS. 



hosts." The rosiilts of the culture experiments are given in the follow- 

 in i>- table: 



Tablk III. — Culture experiments tvith Idark stem rust of Agrostis alba vulgaris. 



The rust is evident!}^ of the black stem rust group {Pucclnla graminis 

 of authors), but contains quite a number of abnormal teleutospores, 

 including mesospores. Many measurements of these spores average 

 27-54 by 16-23yM, mostly 40-46 by 16-18yM. 



Rust of Chloris {Puccmia cJiloridln Diet.). 



The uredoform of this rust is sometimes verv abundant on Chloris 

 vertlc'illata in the Great Plains region, occurring in late summer and 

 autumn. The sori are deep l)rown in color. The uredospores germi- 

 nate very freely and easily. In a number of experiments made in 

 1898 it was found that the uredo on C. vertiGiUata and 0. elegans 

 would readily transfer from either host to the other, but not to other 

 grasses, in several cases which were attempted. In a wat«h-glass cul- 

 ture, made March 18, 1898, of uredospores from C. elegans^ produced 

 from artificial infection in a greenhouse, not only these spores germi- 

 nated freely, but a number of newly formed teleutospores at the same 

 time, an occurrence unusual except in the Lepto-uredinew. Among 

 thousands of cultures made by the writer only one other instance of 

 this kind has occurred. In the summer of 1895 at the Biological Lab- 

 oratory at Cold Spring Harbor, Long Island, both teleutospores and 

 uredospores taken from the same sorus of a rust on Luzula caiwpestris 

 gave good germinations.'' 



Rusts of Willow and Cottonwood (Melampsora). 



Both the uredospores and teleutospores of the rusts of willow and 

 Cottonwood germinate readily, the germ tubes of the latter containing 

 alwa3^s brilliant endochrome. Health}^ leaves of either cottonwood or 

 willow placed in a damp chamber have often been infected by the 



« Arthur describes culture experiments made by his assistant, WilUam Stuart, in 

 July, 1898, in which wheat plants were infected with uredospores from this host, 

 but the spores of the infection sori were larger than those of the original material. 

 (Bui. Lab. Nat. Hist. State Univ. Iowa, vol. 4, No. 4, pp. 396-397, 1898.) 



'^The species was, without much doubt, Pucdiiia obscura Schroet. 



