62 BULLETIN 957, U. S. DEPARTMENT OF AGRICULTURE. 
decreasing percentage of spores were kept in a viable condition, until after a lapse of 
a further period of about three weeks the number that germinated readily was negli- 
gible once more. Before the end of four weeks the spores had ceased to germinate. 
Extensive tests of the longevity of urediniospores were made by 
York, Overholts, and Taylor. 40 In one experiment leaves of Ribes 
nigrum, R. vulgar e, and R. reclinatum were placed in bags of mosquito 
netting with the urediniospores outward. The bags were placed on 
three stakes at 6-inch intervals, the lowest one touching the ground 
and the highest 5 feet above the soil. The lowest spores remained 
viable only 6 to 9 days, while the upper ones were viable longest, 65 
days. A 2-day rain began the day after starting the experiment and 
again a 1-day rain two days later. The urediniospores from R. 
nigrum remained viable longest. Again infected leaves of Ribes 
nigrum, R. vulgare, R. cynosbati, and R. glandulosum were put in open 
boxes and exposed for 4 hours to the early morning sun. Viability 
persisted only 15 days. The urediniospores from Ribes nigrum re- 
mained viable longest. Urediniospores on pulled bushes of Ribes 
glandulosum and R. cynosbati hung in the bright sun remained viable 
only 4 days. Spores on leaves of Ribes nigrum dried in a plant press, 
then put in tight Mason jars and stored in an ice-box remained viable 
80 days. Successful inoculations were made with urediniospores col- 
lected 270 days previously and also with urediniospores from dead, 
overwintered leaves of the previous season. The age of the spores is 
not known, but they were certainly overwintered spores (180). It 
was found that viability in tap water persisted at least 169 days 
when the spore-bearing leaves were air dried and kept under slight 
pressure between sheets of heavy glazed paper. When kept out of 
doors but protected from rain, they retained viability for 100 days. 
In 1918 Pennington 41 made a number of tests of the longevity of 1 
urediniospores. In July and August urediniospores on Kibes leaves 
brought into the laboratory and air dried lost their viability within 
a week when tested in drop cultures of tap water. On September 25 
many Ribes leaves were collected and allowed to dry between sheets 
of paper. The second day urediniospores from these leaves gave 
50 per cent germination when tested as above. The leaves were 
left in the dry air of the laboratory. The spores decreased in viabil- 
ity until November 26 when but 1 per cent germinated. After that 
there was no germination. 
These results, showing a longevity ranging from 7 to 270 days 
under varying conditions, indicate the sensitiveness of the uredinio- 
spores to external factors. In addition it is quite possible that the 
physiological condition of the host plant also has a profound effect 
upon these spores. 
4° York, H. H., Overholts, L. O., and Taylor, H. W. The longevity of the sporidia of Cornartium ribicola. 
Seen in manuscript. To be published in Phytopathology. 
* l Pennington, L. H. Op. cit. 
