34 BULLETIN 957, U. S. DEPARTMENT OF AGRICULTURE. 



found infected with the fungus. In 1920, Snell reexamined these 

 islands much more carefully. He again found the fungus on several 

 leaves and decided that it is evidently a case where the aeciospores 

 were blown from infected pines to the islands. The islands are about 

 7 miles from the mainland, so that it appears that the seciospores may 

 be blown this distance and infect Ribes. There appeared to be no 

 reason for thinking the fungus wintered over. At any rate, it must 

 have come from the mainland originally. The islands where the 

 disease was found are very seldom visited, so carriage of spores in 

 this way appears to be eliminated. 



McCubbin (88) found that the seciospores fall about 8 feet in seven 

 minutes in still air. This indicates a very wide potential distribution 

 of these spores by a moderate breeze. 



In 1918, York and Overholts (cited in Spaulding, 145) worked in 

 the White Mountains of New Hampshire in a generally infected 

 region. Much work was done with spore traps and much time spent 

 in examination of Ribes plants which were isolated from white pines. 

 The work proved that the geciospores are distributed for miles to the 

 tops of adjacent mountains approximately 3,000 feet high, that they 

 arrive in a viable condition, and that they are the means by which 

 the disease spreads far and wide to Ribes. 



In 1918, also, Pennington and Snell (cited in Spaulding, 145) 

 worked in the eastern Adirondack region of New York. Spore traps 

 here gave valuable contributory evidence, but study of the distribu- 

 tion of the first generation of urediniospores with reference to neigh- 

 boring white pines gave the best results. Here it was found that 

 spore traps caught jeciospores up to 550 feet from any pines. Within 

 a large area of cultivated land at Essex, N. Y., an intensive study was 

 made by Snell (128) of the first generation of urediniospores. In this 

 area the Ribes were found to have first-generation uredinia sparingly 

 and widely scattered; that is, the seciospores' causing the infection 

 evidently came from a considerable distance. In one case diseased 

 Ribes were found three-fourths of a mile from any white pine. 

 Several others were found at smaller distances from any pine trees. 

 It was concluded that the seciospores came from a distance of not less 

 than three-fourths of a mile and probably much farther. 



These conclusions concerning the wide spread of seciospores in the 

 two localities were arrived at independently and without the knowl- 

 edge by either party of what conclusions had been reached by the other. 



In 1919, Snell (128) found near Rush Lake, Minn., infections on 

 Ribes leaves which were 13>i miles from the nearest pine and about 

 3 miles from the nearest known diseased pine. Many such infections 

 were found in the same general area which were half a mile or more 

 from any pine. These infections were found developing when the 

 first generation of uredinia appeared throughout that general in- 



