Viability of Uredinio spores 
/V 
/ 
Hasse. The method pursued in this experiment was as follows: 
Silk threads were stretched across an aluminum wire frame (B. 
& S. No. 20) 2 y$ inches square, with legs 1 % inches high en- 
closed in glass stockings of the same height. These frames were 
placed in ordinary preparation dishes, 2 inches high and 3 % 
inches in diameter with loosely fitting covers resting on a 
shoulder ; and sterilized in the autoclave. These dishes were then 
filled with the sulfuric acid solution up to the shoulder of the 
dish so that the threads were about one-fourth of an inch from 
the liquid. The leaves with rust pustules were placed on these 
threads. 
These dishes were placed in larger Koch moist chambers 
with ground glass lids, and the solution poured into them until 
the liquid in both dishes was the same level. The covers of the 
smaller dishes were then quickly removed and the lids of the 
outer dishes vaselined and made air-tight (fig. 3). 
Fig. 3. — Relative humidity chambers, with accessories used in 
viability experiments. 
For the various sulfuric acid concentrations and respective 
relative humidities, the table published by Stevens 1 was used. 
The specific gravity of all solutions was determined by a Twadell 
hydrometer, with the temperature of the solution at 15° C. At 
the conclusion of the experiment, the solutions were rechecked 
at the same temperature and in no case was there a variation of 
more than one or two points on the Twadell scale. 
Incubation chambers. — Owing to the large amount of rust 
material needed for the experiment, and the desirability of main- 
taining a constant temperature during incubation, the following 
apparatus was used. The top of a “Wisconsin temperature tank” 
3 Stevens, Neil E. A Method for Studying the Humidity Relations of 
Fungi in Culture. Phytopathology 6:428-432. 1916. 
