WHITE-PIXE BLISTER RUST. 33 



Observations by Pennington " on the jpcia showed that more aecia 

 were produced per canker and many new cankers were fruiting in 

 1919, so that more aeciospores were produced that year than in 

 1918 in the Adirondacks. Observations on the first generation of 

 uredinia and the results of spore-trap work indicated, howxver, that 

 not as many aeciospores were set free in 1919 as in 1918. This is 

 supposed to have been due to heavy rains, which beat them down 

 from the air. The distribution of the first generation of uredinia 

 showed that the raciospores were as widely disseminated in 1919 as 

 in 1918. 



DISTANCE OF DISSEMINATION OF THE .ECIOSPORES. 



As is true of many of the more difficult points in the life history of 

 Cronartium rihicola, European statements concerning the distance 

 that the aeciospores are distributed are based apparently mostly on 

 personal opinions. The value to be attached to these statements 

 seems to rest on the known excellence, or the reverse, of the pub- 

 lished work and judgment of the writer who is being considered. 

 European mycologists have mentioned a number of instances where 

 this fungus appeared on Ribes which were said to be far removed from 

 white pines. But some of these cases were later found to be actually 

 much nearer diseased white pines than was at first supposed. Tubeuf 

 (166) has stated that the aeciospores spread the disease up to 500 

 meters or more. On the other hand, a considerable number of 

 definite recommendations for separation of the alternate hosts set a 

 distance of only 30 to 100 meters (131, p. 41-42). 



In North America earlier field experience indicated that the 

 aeciospores spread the disease for rather short distances from their 

 source. It was recognized from the- beginning that these spores are 

 exceedingly light and well adapted to wind dispersal, and it was stated 

 that our knowledge of their dispersal was very limited. Special 

 efforts have been made for three seasons to gather more data on this 

 problem. 



Posey, in 1917, set bushes of Ribes nigrum in a salt marsh at Kittery 

 Point, Me., at varying distances from infected pines before uredinia 

 were formed. Some infection resulted from reciospores upon Ribes 

 plants more than a quarter of a mile from any white-pine trees. 

 The infecting spores probably traversed several hundred yards addi- 

 tional, as the nearest pines were not known to be diseased. The 

 heavily infected area was about l\ miles distant, and the infecting 

 spores may easily have come that distance. 



Posey also examined the islands of the Isles of Shoals, off Ports- 

 mouth, N. H., for the presence of Cronartium rihicola. H^e found no 

 pines, but a number of Ribes hirtellum plants. A few leaves were 



1' Pemiiiifrton, L. n. Op. cil. 



46103°— 21— Bull. 957 3 



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