62 BULLETIN 957^ U. S. DEPARTMENT OF AGRICULTUEE. 



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.^" In one experiment leaves of Ribes 

 nigrum, R. vulgare, 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*^ made a number of tests of the longevity of 

 urediniospores. In July and August urediniospores on Ribes leaves 

 brought into the laboratory and air drie d 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. 



« York, H. H., Overholts, L. 0.,and Taylor, M. W. The longevity of thesporidia of Cornartiuinribicola. 

 Seen in manuscript. To be published in Phytopathology. 

 « Pennington, L. H. Op. cit. 



