Sept, a, 1918 
Pinon Blister-Rust 
419 
Table I .—Inoculations with ozcio spores and urediniospores of Cronartium occidentale 
at Washington , D. C. 
.Eciospore inoculations. 
Urediniospore inoculations. 
Host species. 
Plants 
inoculated. 
Plants 
infected. 
Plants 
uninfected. 
Plants 
inoculated. 
Plants 
infected. 
Plants 
uninfected. 
Ribes americanum a . 
4 
I 
3 
9 
5 
4 
Ribes aureum . 
6 
3 
3 
8 
4 
4 
Ribes coloradense . 
0 
0 
0 
2 
2 
0 
Ribes giraldi . 
0 
0 
0 
I 
1 
0 
Ribes glandulosum . 
1 
0 
I 
2 
1 
1 
Ribes malvaceum . 
0 
0 
0 
2 
1 
1 
Ribes nigrum a . 
*5 
0 
*5 
22 
2 
20 
Ribes odoratum &. 
32 
16 
16 
45 
28 
17 
Ribes sanguineum . 
0 
0 
0 
I 
0 
1 
Ribes sp. (?). 
IS 
0 
15 
8 
3 
5 
Grossularia inermis . 
10 
3 
7 
10 
5 
5 
Grossularia missouriensis. 
5 
0 
5 
7 
1 
6 
Grossularia reclinata c . .. 
0 
0 
0 
1 
0 
1 
Total. 
88 
23 
65 
118 
53 
65 
a Plants of R. americanum and R. nigrum inoculated with uredionispores were showered daily with 
spores for several days. 
b R. odoratum was used almost exclusively when conditions were unfavorable; hence the percentage 
of uninfected plants of this species is misleading. 
c The plants of G. redmata were apparently a hybrid between this species and G. hirtella. 
In addition to the inoculations made in the greenhouses at Wash¬ 
ington, a number of plants of Ribes aureum were inoculated in the open 
at Denver and at Bayfield, Colo. Nearly all of these were successful, 
uredinia and telia being produced in abundance in most cases until in 
late October, when the heavy frosts came. Attempts to inoculate 
R ., americanum and garden currants and gooseberries in the open at 
Denver and at Bayfield met with failure. 
INOCULATIONS WITH UREDINIOSPORES 
At Washington, D. C., inoculations with urediniospores were suc¬ 
cessful on Ribes americanum , R. aureum , R. color adense, R. giraldi , 
R. glandulosum, R. malvaceum , R. nigrum , R. odoratum , Ribes sp., Grossu- 
laria inermis , G. missouriensis , and G. reclinataXG. hirtella . On plants 
of the R. aureum type many of the infected areas enlarge rapidly on the 
leaves, and the infection often spreads from leaf to leaf on the same and 
adjoining healthy plants. The uredinia in heavy infections are borne 
close together and eject spores in such masses that the leaf tissue appears 
to be covered. On plants of R. malvaceum , of G. inermis , and of G. mis- 
sowriensis infected areas enlarge rather slowly and do not usually pro¬ 
duce uredinia or spores in abundance. The fungus sometimes spreads 
to new areas of diseased leaves and even to new leaves on infected plants 
of G . inermis , but has not been known to do so on plants of R. mal- 
vaceum or of G. missouriensis . No plants of R. americanum or R. nigrum 
