WHITE-PINE BLISTER RUST. 55 
THE UREDINIA AND UREDINIOSPORES. 
GENERATIONS OF UREDlNIA. 
In 1918, Pennington 34 and Snell investigated the number of genera- 
tions of uredinia of Cronartium ribicola produced in the Adirondack 
region, and the weather conditions that might influence their pro- 
duction. Ribes rotundifolium, R. cynosbati, and R. glandulosum 
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 seciospores or those adjacent to them. Drought 
from July 18 to July 28 caused most of the infected leaves to drop 
from the bushes of Ribes cynosbati 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 Ribes. 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 18 
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 34 found that the generations of uredinia were 
not as distinct at Lewis, N. Y., as they were in 1918. The first 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 serial 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 
s< Pennington, L. H. Op. cit. 
