VHITE-PINE BLISTER RUST. 47 
slowly at first, but later developed strong germ tubes in considerable 
quantity. Scarcely a spore in water germinated. As a result of his 
extensive experience with the rusts, Klebahn says : 
... in other words, I believe it possible for spores which do not germinate in 
water to infect leaves of the host plant, and it seems to me to be expedient to distin- 
guish between "infection power" and "viability" of spores more sharply than is 
ordinarily done. 
Gravatt had experiences somewhat similar to the above in his in- 
oculations with urediniospores of Cronartium ribicola in 1917. So 
pronounced has been our general experience in this regard, that many 
germination and longevity culture tests made in 1918 and 1919 were 
duplicated by check inoculations on favorable hosts so far as possible. 
LOCATION OF THE INFECTIONS ON RIBES PLANTS. 
SORI ON THE LEAVES. 
The usual place for uredinia and telia of Cronartium ribicola to 
form is on the lower side of the Bibes leaf blade. It is rather excep- 
tional for them to appear elsewhere. Nevertheless, they are occa- 
sionally found on the upper side of the leaf blade. They have been 
noted there by Gravatt in the greenhouse and by several out-of- 
door workers on Block Island. The following species have been seen 
with uredinia or telia on the upper leaf surface: Ribes alpestre, R. 
aureum, R. cereum, R. fasciculatum, R. fontenayense, R. Mrtellum, 
R. odoratum, and also the horticultural varieties R. aureum var. 
Utah Yellow and R. vulgare var. White Imperial. It must not be 
concluded that because fruiting bodies are found on the upper surface 
of leaves that the infection took place there. On the contrary, in 
every case seen, it was very evident that the fungus had attacked 
the infected leaf beneath, and the attack had been so intensive that 
some sori were pushed through to the upper surface. There never 
were as many sori on the upper surface as there were on the lower 
one, nor were they so old. 
Some inoculations have been made in Europe to determine if infec- 
tion may take place on the upper surface of Ribes leaves. So far 
as known to the writer they are here summarized : 
In 1913 Ewert (37) brought four potted plants of Ribes nigrum 
into the greenhouse. On April 10 he inoculated the leaves of one 
branch of plant 1 on the lower surface only with fresh seciospores. 
The plant was inclosed in a glass cylinder as a moist chamber. 
Another branch was used as a check. On April 28 the inoculated 
branch bore uredmia upon 11 leaves. On April 15 he inoculated 
the leaves of a third branch, but did not inclose it in a moist chamber. 
On April 26 there was no sign of infection, and it was then inclosed 
in a moist chamber. On May 20 all the inoculated leaves bore 
uredinia. The control remained healthy. 
