42 
BULLETIN 957, IT. S. DEPARTMENT OF AGRICULTURE. 
tried, but is unsatisfactory because the tender leaves of the inoculated 
plants are liable to scald in hot weather. Hunt (57) tested a form 
of the iceless refrigerator for this purpose. This is a modification 
of the field moist chamber described by Keitt (61, p. 540-541), 
without a continuous water spray. It is essentially a framework 
large enough to receive several potted plants, on top of which a large 
pan of water is placed. Around the framework is fitted a loose 
curtain of heavy cheesecloth completely surrounding the framework 
on the sides and extending from the water in the pan on top to the 
ground. In use, the cloth is wet thoroughly and the water in the 
pan keeps it wet. This keeps the air within the chamber saturated 
with moisture and cool, which is the desired condition for the plant. 
This has been very successful even in the hottest summer weather 
and has the desirable qualities of durability, cheapness, portability, 
and simplicity. 
Clinton (12) has recently reported the successful inoculation of 
plucked leaves of Ribes in moist chambers. This is an old method 
with the rusts, and was used by Barclay in India as early as 1887 (4). 
Clinton has apparently developed this method to a point of maximum 
efficiency. It has not been used in the investigations by the writer 
and his associates, the preferred method being to retain natural 
conditions as far as possible in making susceptibility tests. 
FACTORS CONTROLLING THE INFECTION OF RIBES. 
Among the factors controlling infection of Ribes by Cronartium 
ribicola may be mentioned moisture, sunlight, age of leaves inocu- 
lated, and age of inoculum. 
Frequent allusions are made by investigators to the need for 
abundant moisture in producing the infection of Ribes by secio- 
spores and urediniospores of Cronartium ribicola and in spreading 
the fungus on Ribes. 
In 1904, Aderhold (1) performed a series of experiments to deter- 
mine the influence of moisture upon the infection of Ribes vulgare 
by aeciospores of Cronartium ribicola. He had two inclosed cells, 
the air in one of which was -moistened by artificial rain, while in the 
other it was kept relatively dry; he had similarly arranged plats 
open to the free air. The conditions in these cells and plats he 
summarized, as in Table III. 
Table III.- — Conditions in cells and plats of Aderhold' s experiments. 
Experiment. 
Air. 
Temperature. 
Moisture. 
Amount 
of light. 
1 . Rain cell 
High 
Small. 
2. Dry cell 
.do.... 
Slight 
Do. 
3. Open rain plat 
Great. 
do 
Do. 
