64 bulletins' 957, IT. S. DEPARTMENT OF AGRICULTURE. 



mycelium. Each cell regularly puts forth a stout sterigma on which 

 the very thin walled, globular sporidium soon develops. The 

 sporidium has a tiny papillalike swelling where it was attached to the 

 sterigma. The sporidia are 8 to 10 microns in diameter (20). The 

 germ tubes of the teliospores, if developed under water, may not 

 form promycelia but extend elongated hyphse (20) . Under favorable 

 conditions a high percentage of the teliospores may germinate, but 

 because of their aggregation into columellse it is impossible to make 

 an exact count of the germinating spores. Cooling on ice stimulates 

 viability markedly. 



LONGEVITY OF THE TELIOSPORES. 



The longevity of the teliospores of Cronartium ribicola does not 

 seem to have received as much attention as that of the seciospores 

 and urediniospores. Gravatt and Taylor made tests with telio- 

 spores in 1917 similar to those described as made by them with 

 seciospores and urediniospores. (See Table II.) Weekly tests 

 showed that germination persisted in lot B 35 days, while it lasted 

 56 days in lot A. Saprophytic fungi attacked the lot kept on the 

 window sill, so that the test probably does not show the longevity 

 of healthy teliospores. 



York ^^ in 1918 found that teliospores were still capable of germi- 

 nation in tap water after being kept on the plucked leaves 65 days 

 out of doors in the shade. A similar test of teliospores kept in the 

 dark in the laboratory gave germination for 90 days. 



THE SPORIDIA. 

 SEASON or PRODUCTION OF THE SPORIDIA. 



The sporidia may be produced as soon as the telium is mature, if 

 there is sufficient moisture in the air for a number of hours. 



The telia may remain alive on dry dead leaves out of doors for 

 more than 65 days, so that sporidia might be produced well into the 

 winter in mild seasons, thus prolonging the danger season for pines. 



DISTANCE OF DISSEMINATION OF THE SPORIDIA. 



In work with spore traps by Pennington ^^ and Snell in 1918, 

 sporidia were caught up to 60 feet from very heavily infected Ribes 

 bushes. This was in the eastern Adirondacks, about 8 miles from 

 Lake Champlain. Hundreds of pines were examined for infections. 

 In no case was infection found on pines as far as 200 feet from Ribes 

 plants. Pennington made a study of nine outbreaks in pines in the 

 Adirondacks. The infection on pines was confined to an area 

 within 100 to 200 feet of the Ribes plants which infected the pines. 



« York, H. H. Op. cit. 



■16 Pemiington, L. H. Op. cit. 



