WHITE-PINE BLISTER RUST. 51 
R. vulgare by Marshall. None were found by Unger (176) on the upper surface of 
leaves of 7?. alpinum nor by Taylor on R. americanum, R. aureum, R.. carrierii, R. 
culvenvellii, R. fasciculatum, R. nigrum, R. reclinatum, R. speciosum, and R. (tenui- 
florum) aureum. Stomata were found only on the lower surface of cotyledons of R. 
fasciculatum and R. missouriense, the only ones examined by Taylor. Stomata were 
found by Taylor to be not uncommon on petioles of R. americanum, R. aureum, R. 
carrierii, R. culverwellii, R. hirtellum, R. inerme, R. nigrum, R. odoratum, R. reclina- 
tum, R. sanguineum, R. speciosum, R. succirubrum, R. (tenuiflorum) aureum, and R. 
vulgare. None were found on petioles of R. curvatum and R. fasciculatum. Janczewski 
(60) states that stomata are present on the young stems of R. petraeum. A few stomata 
were found on young stems of R. aureum, R. hirtellum, R. nigrum, R. odoratum, R. 
reclinatum, R. succirubrum, R. (tenuiflorum) aureum, and R. vulgare. None were found 
on the stems of R. carrierii and R. fasciculatum. These findings compare well with 
the inoculation results, if stomata are the avenue for infection. It is perhaps to be 
expected that infection may be produced on the upper surface of the leaves, but only 
very rarely. Colley (20) found young uredinia forming in the substomatal spaces, 
which would indicate that infection took place in that vicinity and presumably 
through the stomata. York 32 found germ tubes of seciospores entering the stomata of 
leaves of Ribes cynosbati, R. glandulosum, and R. nigrum. 
VARIATIONS IN APPEARANCE ON RIBES LEAVES. 
The study of great numbers of Ribes leaves infected in the green- 
house and of very numerous specimens of diseased leaves collected 
in the field from Maine to Minnesota, during the past ten years, has 
revealed some distinct variations in the appearance of the fungus 
and of the diseased leaves of different species and varieties of Ribes. 
Previous study of such differences seem to have been made chiefly 
by Hennings (52, 53). 
BLISTERY APPEARANCE OF THE UREDINIA. 
In August, 1916, there occurred a very hot, dry period in New 
England. This was followed by the finding of a few very peculiar- 
looking uredinia on Ribes nigrum and R. vulgare. Under a hand lens, 
the uredinia were not of the usual mealy appearance, but looked more 
like tiny blisters. Examination showed that the epidermis of the 
leaves had become toughened, so that the uredinia did not burst 
through it, as they usually do, but pulled it loose from the inner leaf 
tissues and in this way actually formed small blisters. The uredinio- 
sporcs never broke through it. From the weather conditions pre- 
ceding and at the time this occurred it is believed that the dry, hot 
weather rendered the epidermis tougher than usual. It is a rare 
occurrence, as only a few cases have been noted. In 1916, one speci- 
men came from each of the States of Massachusetts, Maine, and Ver- 
mont. In 1917, a single case was found in New Hampshire. Hedg- 
cock noted this in 1919 upon artificially inoculated Ribes bushes on 
Block Island. Recently, blisters have been noted on R. auruem and 
R. fasciculatum in the greenhouse. 
3* l r ork, H. H. Op. cit. 
