WHITE-PINE BLISTER RUST. 57 
were protected by surrounding trees or other objects, the rust spread 
little or not at all. In other words, where moisture was plentiful 
through the season, the distance of spread by urediniospores was 
governed by factors controlling the free access of the wind. In 
Essex County, N. Y., drought prevailed through July and August 
in 1918. Here Pennington 36 worked with spore traps and Snell (128) 
gave special attention to a study of the spread of the uredinial stage 
on Ribes. The Ribes of this section were largely Ribes rotundifolium 
and R. glandulosum. Here the rust spread in most instances only 
to adjacent leaves from those first infected on a given bush. The 
spore traps here caught urediniospores only at a very short distance, 
50 feet or less. 
In 1919, York (cited in Spaulding, 146) caught urediniospores up 
to a distance of 3,400 feet in an open location, but they did not 
germinate. Urediniospores caught at 3,200 feet did germinate. 
Pennington 36 caught urediniospores up to 156 feet. 
AGENTS DISSEMINATING THE UREDINIOSPORES. 
Wind has been supposed to be the principal agent distributing 
the urediniospores of Cronartium ribicola. While this supposition is 
correct in the main, other agents are concerned in the matter. 
Hennings (53) says that sprinkling diseased Ribes plants with a 
strong stream of water carries urediniospores from plant to plant. 
Rain accompanied by high wind is known to carry spores of some 
plant diseases (38, 44). It is entirely possible for this to occur with 
any spore capable of wind distribution, as in the present case. 
In 1917 Gravatt and Marshall (45) made studies in the experi- 
mental greenhouse at Washington, D. C. They found that weevils, 
snails, slugs, and sow bugs fed on the uredinia and telia of Cronartium 
ribicola on the diseased plants. The ingested urediniospores lost 
their viability to a large extent, but not entirely. 
In the same year Gravatt and Posey (46), working at Kittery 
Point, Me., found that gipsy-moth larvae feed quite freely upon leaves 
of Ribes hirtellwn and R. vulgare and that in some cases the only 
infected leaves were those which had been partially eaten by insects, 
indicating that they carried the spores which infected the leaves. 
The insects were found carrying viable urediniospores on their bodies. 
There can be no doubt that these insects play an important role in 
the local distribution of this fungus within the gipsy-moth infested 
area. 
Studies by Snell (127) at Lewis, N. Y., in 1918,. show that a large 
number of insects visit Ribes plants during the season when the rust 
is present upon the leaves. The spore-laden insects were inclosed 
in chambers with the tips of Ribes glandulosum plants, and infection 
36 Pennington, L. H. Op. cit. 
