242 abstracts: plant pathology 



The so-called stem rusts of wheat, barley, rye, and oats are undoubt- 

 edly "biologic forms" of the same species, Puccinia graminis Pers., 

 and though many of them are highly specialized an interchange of hosts 

 may often be induced by special cultural methods. By gradual varia- 

 tion and adaptation to varying conditions, a rust species widely distrib- 

 uted may form a number of strains or types differing in physiological 

 reactions. 



In successive cultures of the uredospores of six different grain rusts, 

 the fifty-second generation was apparently as vigorous as the first in 

 spite of the absence of the aecidium during this period, no "invigoration" 

 having been necessary for this length of time. The uredo of several 

 of the rusts may survive the 'winter in latitudes as far north as St. Paul, 

 Minn. Rust spores may be carried from one region to another for hun- 

 dreds of miles by winds and upper air currents. 



Subnormal temperatures, delaying and lengthening the heading and 

 early flowering of period the wheat and furnishing conditions most favor- 

 able for spore germination and infection, are believed to have been an 

 important factor, if not the determining factor, for the stem rust epi- 

 demic of 1904 in the Middle Northwest. 



For the prevention of rusts fungicides and soil treatments, as a rule, 

 have proven ineffective, and the only practical method known is the 

 production of rust-resistant varieties through hybridization and selec- 

 tion. To what character resistance is due is not clearly understood. 

 Resistance and susceptibility in cereals, however, are inheritable char- 

 acters, apparently occurring in Mendel ian proportions. In breeding 

 ceieals for resistance, the rust must be present in the breeding plants 

 every year. To insure this special methods of rust propagation must 

 be employed. E. C. J. 



PLANT PATHOLOGY.— Timothy rust in the United States. Edward 

 C. Johnson, Bureau of Plant Industry, Bulletin 224. Pp. 20. 1911. 



Timothy rust was reported from Wisconsin in 1882. There is some 

 doubt concerning the accuracy of this report. It was reported from Iowa 

 in 1891. From 1891 to 1906 no mention of the parasite has been found. 

 In 1906, the rust became epidemic at the Arlington Experimental Farm 

 and since then has been found from Maine to Minnesota, and south 

 to Iowa, Kentucky and Virginia. 



Rust on timothy is similar to Puccinia graminis Pers. on wheat. Ex- 

 perimental results demonstrate its identity with the rust on timothy 

 in Europe. The aecidial stage is not definitely known. Early indica- 



