MICHIGAN ACADEMY OF SCIENCE. 137 



(Dc.) Wint. oil wheat and rye that the iiiiiiiiiiiiiii temperature for 

 germiuation was '2° C. aiid the maximum ol° C. For Puccinia coro- . 

 nata Corda. on oats the minimum was 7° (\ and the maximum was 

 30° C. 



Other factors besides temperature enter in controlling jiermina- 

 tion but none are as general except moisture. Thus Marshall ^Vard 

 lias found that the spores of the brome rust germinate readily in 

 light or in darkness, in red but not as well in blue light, in water 

 containing green Algae, fibers of paper-pulp, and even germinating 

 spores of other fungi, provided the temperature does not rise above 

 the maximum and the spores are mature and fresh. W. Robinson 

 has found^ that the germ tubes of the sporidia of PuecinUi malva- 

 cearum Mont, grow away from the light. I also understand that F. 

 D. Fronime has reported the same for the germ tubes of the uredo- 

 spores of Puccinia rliamni (Pers.) Wettst. {Puce, coronata Corda.) 

 to the Botanical" Society of America in December, 1914. 



In experiments with decoctions of the host, Marshall Ward was 

 not able to find any effect produced by raw or cooked extracts of the 

 host upon the germination of rust si)ores. Robinson, likewise, 

 found that, when germinated in the dark, pieces of mallow leaf had 

 no effect upon the sporidia of Puccinia malvaccarum Mont. 



Moisture, of course, is a factor of prime importance. All workers 

 with the rusts have recognized the fact that germination will take 

 place only in the presence of moisture. Fromme finds' that, even 

 with a humid atmosphere of 93 per cent infections take place only 

 sparingly and, to obtain good infection, the saturated atmosphere 

 of a belljar is required. Klebahn has worked with the teleutospores 

 of Puccinia graminis I'ers, Puce, phragmitis (Schum.) Korn., and 

 Puce. Magnusiana Korn.^ In all these, the teleutospore is supposed 

 to germinate only after wintering. He found, however, that the 

 C'ondition for the germination of the teleutospore is principally an 

 alternate wetting and drying. Cold is not necessary and in fact, acts 

 as a hindrance. 



The work upon which this paper is based was mostly done dur- 

 ing the summer of 1914 and was initiated, as most of sucli work has 

 been, by the diificulty of obtaining germination during the summer 

 months. The rust Avhich was under investigation at the time 

 {Puccinia coronata Corda.) was first tested as to its germiuation 

 at different temperatures. Other rusts were then investigated to 

 see how far this temperature relation held. The tests were all made 



.5. Annals of I'.otanv 28 :330. 



(i. Anicr. Jour of Hut. 2 :.S2. 



7. Torrpy Bot. Club Bull. 40 :.501. 



8. Zeits. fiir rtlanzenkrankheiten 24 :1. 



