FIRST APPEARANCE OF RUSTS IN THE SPRING. 55 



SoLitli where fresh uredos of botli Puccinia graminis and P. ruhigo- 

 vera forms are plontifid at this time of the year. This furnishes 

 substantial evidence that KU'balui's suppositions are correct, and 

 rust spores may be consi(ler(Ml fairly universal in chstribution. 



VIABILITY OF THE UREDOSPORE. 



That spores can resist desiccation in air and maintain their via- 

 bility when transported long distances has been proved by Bolley 

 (24, p. 892). In July, 1898, he demonstrated that uredospores of 

 Puccinia ruhigo-vera, exposed for 1 2 days on a dry watch glass placed 

 in the sunlight, would germinate 80 to 100 per cent, and on August 4, 

 spores placed in a similar place for 21 days would germinate from 

 5 to 10 per cent. July 25 and August 4, 1898, respectively, the 

 same investigator proved that the uredo of P. graminis would give 

 "good" germination after being exposed for 12 days on a watch 

 glass in direct sunlight, and gave 8 to 15 per cent germination after 

 21 days on a watch glass in a similar position. 



Ward (102, p. 13) found that uredospores of Puccinia dispersa ger- 

 minated after being kept dry for 61 days; and Miss Gibson, working 

 in his laboratory, kept secidiospores of Phragmidium for 54 days and 

 uredospores of chrysanthemum rust for 94 days, when they still 

 germinated. Carleton (31, pp. 21, 22), February 3, 1898, germinated 

 uredospores of P. crypfandri collected in Oklahoma, October 8, 1897, 

 and kept as herbarium specimens, and got successful infection on 

 Sporoholus airoides from inoculations made February 6 from the 

 same material. This is an extreme case of the viability of the 

 uredospore when kept in a dry condition. 



The authors have numerous times shipped uredo material of the 

 cereal rusts through the mails from Minnesota to Washington, D. C, 

 and \ace versa, and from Texas to Washington, D. C, and have 

 experienced no difficulty in producing successful infection on grow- 

 ing plants, even after these spores had been lying in the laboratory 

 for several days after their arrival. The uredospore is thus seen to 

 be sufficiently resistant to bo transported long distances in a dry con- 

 dition by either the wind or other agencies. 



FIRST APPEARANCE OF RUSTS IN THE SPRING. 



From the facts cited concerning the viability of the uredospore 

 and its almost universal distribution, the first spring infection of 

 grains in northern latitudes and the infection of grains far removed 

 from the ff'cidial liosts of the rusts may be explained. Careful 

 observations on the fu'st appearance of rusts in the spring were made 

 at Minnesota in 1907, 1908, and 1909. In 1907, Puccinia ruhigo- 

 vera on winter wheat was common up to the middle of April, when 



216 



