136 SEVENTEENTH REPORT. 



SOME FACTORS CONCERNED IN THE GERMINATION OF 



RUST SPORES. 



BY E. B. MAINS. 



Workers with the rusts have, for a long time, been troubled with 

 the so-called "erratic" or ''capricious" oermination of the spores of 

 these fungi. Such were the words usually used to explain the un- 

 certain germination and infection by the uredo- and aecidiospores 



of the rusts. 



Eriksson, while working upon the grain rusts/ found considerable 

 diflQculty in germinating the aecidiospores of Puccinia graminis Pers 

 during the summer for, although spores of different maturity were 

 sown in solutions of different kinds, no results were obtained. Fin- 

 ally in the late summer, he came to the conclusion that chilling the 

 spores might have some effect. He found that by placing the 

 spores on melting ice which finally came to the room temperature 

 lie obtained the best results. Upon having similar difficulty with 

 the uredospores of Puccinia glumarmn (Schw.) E et H., he tried 

 the same method with like success. Marshall Ward in his work 

 upon the brome rust- found that a number of factors contributed to 

 this "capricious" behavior. He found that the uredospores of the 

 brome rust Puccinia dispersa (Erikss. ) germinated best at about 20° 

 C. with a maximum limit of germination at 20-27.5° C. and a mini- 

 mum at about 10-12° C. He remarks that it had been largely taken 

 for granted that uredospores would germinate at almost any tem- 

 perature during the summer. It was due to the failure to obtain 

 infection under conditions which pointed to the tem])erature as a 

 cause which led him to investigate the subject. Melhus, working 

 on the Oomycetes, found that a low tem])erature was important for 

 «pore germination and infection in this group. He later applied his 

 methods, as used in that group, to others.^ Among the rusts, he ob- 

 tained abundant infection with Puccinia hclanthia (Schw.) at l-t" 

 C. and with I'licclnUi coronata Corda. at 10° C. and with Puccinia 

 soff/lii Schw. at 1S° C. E. C. .lohnson, working on the cereal rusts* 

 found for Puccinia graminis Pers. and for Puccinia ruhigovera 



1. Zolts. fiir Pflanzi-nkniuklioitou 4 Mjfi. 140. Ift". 2r>7. 



2. Annals of Hotanv IC :2.33 ; Annules Mvcologici 1:132. 



3. rii.vtdpatholoK.v 2 :litT. 



4. Abstract In riiytopathology 2:47. 



