WHITE-PINE BLISTER RUST. 43 
Aderhold placed his experimental plants in these cells and plats 
on April 16. On May 6 all of the plants were heavily dusted with 
seciospores, and half of those in each cell and plat were put under 
conditions opposite to those they were in before inoculation. The 
plants from the closed rain cell when inoculated and replaced in the 
same cell took the disease heavily. Those from the closed dry cell 
when inoculated and placed in the closed rain cell also took the 
disease heavily. Those transferred from both the rain and dry 
cells to the dry after inoculation showed no infection. All the plants 
kept in the open plats failed to take the disease. It is apparent 
from his results that infection depends upon an atmosphere that is 
nearly saturated with moisture. 
Experience in the greenhouse has shown that it is necessary to 
have abundant moisture on the leaf surface for infection to succeed. 
The leaf itself must be wet, without having large drops of water 
collect. This moisture must be retained for some time by keeping 
the surrounding air saturated with water vapor. Gravatt made a 
series of parallel tests, part of the inoculated plants being kept under 
bell jars 2 hours, part of them 7 hours, and another part 24 hours. 
Infection occurred with the 7-hour and the 24-hour plants, but not 
with the 2-hour tests. The writer made a series of inoculations in 
the greenhouse with seciospores without putting the plants in moist 
chambers. Not one infection resulted within 14 days, the usual 
time necessary to reach full fruiting condition. The plants were 
then put into moist chambers for 48 hours, and fair infection resulted 
from the spores put on the leaves 14 days before. Ewert (37) per- 
formed a similar experiment in 1912 with the same results, as did 
Werth (177) in 1915 and York 25 in 1919. McCubbin in 1916 inocu- 
lated two leaves on each of seven shoots of a Rites nigrum plant. 
Two of the shoots were put in a moist chamber for 48 hours. The 
remaining five shoots were left uncovered. The leaves of only the 
two inclosed shoots developed infection. 
It is equally necessary to have plentiful moisture for infection to 
occur out of doors. Hennings (53) found a severe outbreak of the 
disease on Bibes during a dry time in the Dahlem Botanical Garden, 
but he attributes the intensity of the attack to the daily watering 
(sprinkling) of the bushes. Ewert (35) says, "In the summer of 
1902, moisture, the important factor for infection, was not lacking, 
so all conditions were favorable for the spread of the Cronartium. " 
Schellenberg (123) attempted to inoculate Bibes bushes with secio- 
spores from Pinus cembra in the open air. He attributes his failure 
to produce infections to the bright sunny weather prevailing at the 
time. In 1910, the writer (131) inoculated Ribes leaves with fresh 
» York, H. H. Op. cit. 
