RELATION OF SOME RUSTS TO THEIR HOSTS 191 
quartz sand prepared as above and the jars were then placed in the 
greenhouse. The various solutions were used to water the plants. 
After 35 days, the plants were inoculated and placed in a moist chamber 
at 20° C. for twelve hours. 
In both experiments sections through the infected areas showed 
that from about .5-1.2 mm. on each side of the pustules, there was 
no starch in the parenchyma sheaths, although it was present 
in considerable quantities in the rest of the leaf. Beyond this for 
about .2-.6 mm. on each side, the concentration of the starch gradually 
increased until it reached the full concentration of the rest of the leaf. 
Table I 
Effect of Mineral Starvation upon the Development of Piiccinia Sorghi 
Solution 
Condition of Plants 
Number of 
Plants Used 
Number of 
Plants Infected 
Average No. 
Pustules per 
Plant 
Water Culture 
Sand Culture 
Water 
Culture 
Sand 
Culture 
Water 
Culture 
Sand 
Culture 
Sand Culture 
Full solution . . 
— Ca 
green 
yellowish 
green 
dead 
2 
3 
5 
5 
2 
I 
4 
0 
197 
0 
— Fe 
light green 
4 
5 
4 
4 
4 
3 
4 
3 
3 
4 
3 
2 
31 
170 
8 
— CI 
4 
5 
— Mg 
4 
5 
— K 
green 
4 
4 
3 
5 
5 
3 
2 
32 
12 
II 
— P 
dark green 
light " 
- N 
5 
3 
2 
— S 
green 
4 
5 
13 
The results as given in Table I show that mineral starvation does 
not prevent infection of Puccinia Sorghi but only that the amount of 
rust as shown by the number of pustules is less. Starch is prevented 
from forming in the immediate vicinity of the pustules. 
Effect of Light upon Development 
The effect of light upon development of the rusts was studied in a 
set of experiments, the results of which are given below. A number of 
pots of the plants were inoculated under the same conditions Some 
were then placed under belljars in the light, and the rest were covered 
with dark cylinders. After a few days, the plants under the dark 
cylinders were placed in the light and the incubation periods of each 
recorded. 
