WHITE-PINE BLISTER RUST. 55 



THE UREDINIA AND UREDINIOSPORES. 



GENERATIONS OF UREDINIA. 



In 1918, Pennington ^^ and Snell investigated the number of genera- 

 tions of uredinia of Cronartinm ribicola produced in the Adirondack 

 region, and the weather conditions that might influence their pro- 

 duction. Ribes rotund if olium, R. cynoshati, and R. glandnlosum 

 were the principal species used in these investigations. The observa- 

 tions were made in four different localities within 10 miles of the 

 town of Lewis. There were seven periods of uredinial production in 

 1918. The first generation began on May 28, reached its climax 

 about June 12, and then gradually fell off until June 26 to 28, when 

 the second appeared. The third began to appear about July 12 and 

 reached its maximum on July 19 to 22. The second and third crops 

 of uredinia were located almost entirely on those leaves which were 

 originally infected by aeciospores or those adjacent to them. Drought 

 from July 18 to July 28 caused most of the infected leaves to drop 

 from the bushes of Rihes cynoshati and R. rotundifolium, leaving them 

 partly or entirely defoliated. The fourth crop was much smaller, 

 but well marked, and came on August 19 and 20. The fifth genera- 

 tion came on September 12 to 15; it would have been more abundant 

 had not a heavy frost on September 11 killed all the leaves of R. 

 glandulosum and some on the other two species of E-ibes. The sixth 

 crop appeared especially on the second crop of leaves of the earlier 

 defoliated bushes and on fresh green leaves of bushes in sheltered 

 situations. The seventh generation appeared on October 15 to IS 

 on leaves ready to fall. A study of the weather conditions, as noted 

 at Lewis, showed that about two weeks before the appearance of each 

 new generation there was a period of at least 24 hours of rainy and 

 cloudy weather. But not all such periods were followed by new 

 crops of urediniospores. 



In 1919, Pennington''* found that the generations of uredinia were 

 not as distinct at Lewis, N. Y., as they were in 1918. The fu'st four, 

 on May 23, June 21 and 22, July 3, and July 20, respectively, were 

 well defined. A fifth on August 7 and a sixth on August 21 were 

 distinct on some bushes, but in most places overlapped. In general, 

 after August 1, the generations overlapped, because of rain every 

 day or two, so as to become confused with each other. 



SEASON OP PRODUCTION OF THE UREDINIA. 



Like the secial season, the beginning of the uredinial season of pro- 

 duction varies with conditions somewhat, though to a less marked 

 degree. May 16 is the earliest recorded date for mature uredinia. 

 A week after this is the more usual time for them to be found in most 



»< Pennington, L. H. Op. cit. 



