WHITE-PINE BLISTER RUST. 71 
previous winter a single seedling plant of an unknown species bore 
leaves flat on the soil under similar conditions until March 12, 1917, 
when it was brought into the greenhouse and inoculated. It 
promptly took the disease on the overwintered leaves. York 52 found 
Riles glandulosum plants in the spring of 1918 which bore overwin- 
tered leaves that later became infected naturally. In such cases, it 
would be easy to understand that late infections in the fall might lie 
dormant until spring and then produce vigorous uredinia. More 
time is necessary to determine whether this actually occurs. 
As stated previously, infection of petioles by Cronartium ribicola 
is quite common. Early in 1917 Colley (17) discovered that infected 
petioles often had telia and masses of active mycelium as well as 
uredinia in the central pith. This raised the question of the possi- 
bility of such mycelium remaining active until spring and producing 
new uredinia. 
Whether the fungus can live over winter on dead diseased leaves 
seemed unlikely in view of the negative results of Arthur and Petry 
(151) with urediniospores from stems of plants diseased the preceding 
summer, and the negative results of Stewart (151) with material 
overwintered out of doors at Geneva, N. Y. Howitt and McCubbin 
(56) early in 1915 attempted to produce infection by spores which 
remained over winter out of doors on dead Bibes leaves. All of their 
attempts were unsuccessful. In the spring of 1918 York (180) and 
the writer obtained infections with urediniospores overwintered out 
of doors in Massachusetts on dead Ribes leaves, proving that uredi- 
niospores may survive the winter. This was repeated in the spring 
of 1919 by Taylor (157). 
The possibility of infection on Ribes stems was early investigated 
by the writer but with no success. Many inoculations were made on 
young Ribes shoots by the writer and later by Gravatt, Doran (28), 
and York 52 but without success. However, in the summer of 1917, 
Posey and Gravatt (112) discovered fruiting uredinia on the young 
shoots of Ribes Mrtellum at Kittery Point, Me. They inoculated 
other young shoots with seciospores and secured mature uredinia. 
Colley found uredinia in the pith of these infected stems. Gravatt 
later inoculated young seedlings of Ribes fasciculatum in the green- 
house with geciospores and secured heavy infection of the cotyledons. 
In one seedling the fungus also attacked the stem jus.t below the 
diseased cotyledons and developed several uredinia (PI. V, fig. 2). 
Later, however, the plant outgrew the disease. Taylor and York 
have successfully, inoculated stems of several species of Ribes. (See 
p. 50.) 
That Cronartium ribicola overwinters on Ribes is established. 
52 York, H. H. Op. cit. 
