WINTERING OF THE UREDO GENERATION. 49 



He did not demonstrate the wintering of the uredo of Puccinia 

 coronata on oats, P. graminis tritici, or P. graminis avenae, although 

 it is his opinion that P. coronata passes the mnter in the nredo stage 

 in the warm hititiides of the United vStates (30, pp. 49, 57, 64). 



In 1902-3, Christman (32, pp. 103, 104) showed that in the locaUty 

 of jMadison, Wis., the uredospores of Puccinia ■poanim would winter 

 and germinate as late as IMarch 13; of P. ruhigo-vera secalis and P. 

 ruhigo-vera tritici, March 20. Numerous other collections and germi- 

 nations were made tlu-oughout the winter from plants in exposed 

 places, and the author concludes that — 



in the latitude of Madison and mth a period of three months during which the tem- 

 perature scarcely rises above the freezing point, viable uredospores may be obtained 

 at practically any time during the winter. 



In investigations during the winter of 1904-5, BoUey (28, p. 642) 

 obtained a collection of viable uredospores of Puccinia ruhigo-vera 

 in December and January in Kansas, Oldahoma, Missouri, Illinois, 

 Wisconsin, IMinnesota, and North Dakota. Viable uredospores of 

 P. graminis were collected late in October at St. Louis, and December 

 25 at Dallas, Tex. In January — 



quantities of them were being procured upon winter wheat at Riverside, 111. Later 

 some were procured in quack-grass at Lake City, Minn., and a quantity of \iable 

 spores were taken from the leaves of quack-grass and wild barley frozen in the ice at 

 Fargo in March, 1905. 



RECENT EXPERIMENTS ON THE WINTERING OF THE UREDOSPORE. 



During the winter of 1906-7, the authors undertook to establish 

 the extent of viabilit}^ of the uredospore of various rusts in the 

 vicinity of St. Paul, Minn. All material was collected on or near 

 the ^Minnesota Agricultural Experiment Station farm. 



In the early fall suitable plants of Ilordeum juhatum, Agropyron 

 repens, A. tenerum, winter wheat, and fall-sown barley were selected. 

 These were left undisturbed in the open field at the University farm. 

 They had become thoroughly infected by either Puccinia graminis, 

 P. ruhigo-vera, or both. During the fall and winter, collections of 

 uredospores were made from all hosts, selected every month and at 

 times at intervals of two weeks. 



Portions of the various hosts were also collected November 20 and 

 23 (1906); these were kept outside, were buried in snow December 

 10, and left in this conchtion until March 20, 1907. Every month 

 specimens from this supply were tested in the same manner as the 

 material brought from the field. 



All tests were made in distilled water in watch crystals placed under 

 a bell jar and kept at orchnary living-room temperature or a little 

 above. In many instances the percentage of spores tliat germmatod 

 was determined by actual count, but generally rougli estimates only 

 were made. 



88550°— Bull. 216—11 4 



