220 



of investigations were made which showed, as suspected, that the rusts in 

 question do have other means than the teliospore of surviving the winter 

 and that in all likelihood they are able to propagate themselves indefinitely 

 in an asexual manner, and that without serious impairment of vigor. In 

 this paper it is proposed to give the results of this work and to present 

 some field data, chiefly from Indiana, which was made available to the 

 writer by his access to the Arthur herbarium. This data goes to indicate 

 that what is true of the grain rusts is equally true of some others which 

 because of their lack of economic importance have thus far escaped this 

 sort of investigation. 



DURATION OF VIABILITY OF UREDINIOSPORES. 



Before entering on the discussion proper, however, it seems best to 

 treat here two points which have a bearing on what is to follow ; namely, 

 the duration of the viability of urediniospores and the distance to which 

 they may be blown and produce infection. As to the duration of germina- 

 bility in the urediniospore, more work has been done with the grain rusts 

 perhaps than with any other. In the case of Puccima graminis Hunger- 

 ford reports 1 finding germinable urediniospores at Madison, Wis., on timothy 

 in October, November, December, January, and March ; but it does not 

 seem to be at all certain that the spores used on the last named date were 

 wintered spores. On the contrary, it is altogether possible that they were 

 but recently produced. Mercer, 2 however, was not able to find germinable 

 urediniospores of the same rust on the same host during the winter in 

 North Dakota ; and Eriksson and Henning, 3 as the result of several experi- 

 ments with the rust on different hosts, came to the conclusion that the 

 fungus does not pass the winter in the uredinial stage in Sweden. They 

 also came to the same conclusion in regard to P. fflumarum. 4 Bolley"' 

 reported the germination of 8-15% of urediniospores of P. graminis after 

 twenty-one days in dry air in August. The same investigator has shown 

 that the urediniospores of the leaf rust of wheat can be used for successful 

 infection material after thirty days' exposure to the outside air in July, 

 while Freeman and Johnson consider it possible for urediniospores of P. 

 graminis and P. rubigo-vera to survive the winter in Minnesota, North 



'Phytopathology 4:337-338. 1914. 



»1. c. 20-22. 



'Die Getreideroste 38-47. 1896. 



<1. c. 153-159. 



6 Centralblatt for Bakt. Par. und Infekt. 4 2 :893. 1898. 



"Agricultural Science 5:263. 1891. 



