METHODS OF DISTRIBUTION. 13 



It is seen that some of the ])lants l)r()uglit in on January 19 and 

 March 12, notably Nos. 1, 3, 4, 7, and 8, continued to produce uredo- 

 spores. At Ai-hngton, in 1908, fresh rust pustules on new growth 

 of timothy were common after March 15. Undoubtedly the old 

 rust mycelium living in the plants had produced these pustules. 

 S])ores collected on January 20 and March 13, 1908, were found to 

 be viable. 



Similar conditions undoubtedly prevail in other localities of the 

 same latitude and similar climate wJiere this rust is found. How 

 the rust winters fartlier north has not been determined, but in the 

 light of recent investigations ^ it is very probable that it lives through 

 the winter in the uredo stage much farther north than the latitude 

 cited. As shown by specimens sent to the Office of Grain Investi- 

 gations, it seems that teleutospores of this rust are more abundant 

 in northern latitudes than at the Al'lington Experimental Farm, 

 where they were very scarce in 1907 and 1908. At the latter i)lace 

 the parasite Darluca flum (Biv.) Cast, largely prevents the forma- 

 tion of the teleuto stage, as almost every pustule ready to produce 

 teleutospores is attacked by tliis fungus and further development 

 is prevented. However, as the secidial stage, if present, is undoubt- 

 edly rare in this country, the teleuto stage is of doubtful importance 

 in the wintering and dissemination of the rust. 



METHODS OF DISTRIBUTION OF TIMOTHY RUST. 



The rapid distribution of timothy rust in recent years is doubtless 

 due to the dissemination of the uredospore by the usual agencies. 

 Insects have been shown to be carriers of spores,- birds and other 

 animals may carry them from place to place, they may be transferred 

 from one region to another by man through the shipment of rusted 

 timothy hay, etc., but most important is the agency of the wind. 

 It has been shown probable ^ that the uredospores of rusts are dis- 

 tributed by the wind not only from field to field, but, rising into the 

 npper air, are carried by currents for hundreds of miles. With a 

 quantity of uredospores on hand in various localities early in the 

 spring, their distribution thus becomes an easy matter and the 

 general dissemination of rust over large areas is accounted for. 

 Undoubtedly, in the course of a few years, the distribution of this 

 rust is to be expected over all timothy-growing sections where con- 

 ditions are favorable for its development. 



With the ultimate dissemination of rust over the greater part of 

 the timothy area a practical certainty, methods of preventing any 



• Freeman and Johnson, loc. clt. 



2 Johnson, Edward C. Floret Sterility of Wheats in the Southwest. Phytopathology, vol. 1, 1911, p. 18. 



2 Freeman and Johnson, loc. cit.; and Klebahn, H., Die wirtswechselnden RostpUze, 1904, pp. 68-72. 



224 



