192 E. B. MAINS 
Puccinia Coronata 
Experiments 8, g, and 10. — In these experiments inoculation was 
accomplished as stated above and the results obtained are given in the 
following table. 
Table II 
Effect of Light upon Development of Puccinia Coronata 
Experiment 
Pot No. 
Time in Dark 
Time in Light 
Incubation 
Retardation 
8 
C 17. 1 
C 17.2 
c 17.3 
C 17.4 
c 17.5 
C 17.6 
5 days 
5 " 
18 " 
18 " 
10 days 
10 " 
10 " 
10 " 
10 days 
10 " 
15 " 
15 
died, no infection 
died, no infection 
5 days 
5 " 
9 
C 17.7 
C 17.8 
C 17.9 
C 17.10 
C 17. II 
C 17.12 
7 " 
7 " 
20 " 
20 " 
10 " 
10 " 
6 " 
6 " 
7-10 days 
7-10 " 
12-13 " 
12-13 
no infection 
6-7 " 
6-7 " 
10 
C 17.13 
C 17.14 
C 17.15 
C 17.16 
C 17.17 
C 17.18 
7 " 
7 " 
20 " 
20 " 
10 " 
11 " 
5 " 
5 " 
10 days 
11 " 
13 " 
.^3 " 
no infection 
2-3 " 
2-3 " 
The results of these experiments show that in the absence of light 
the development of Puccinia coronata is retarded and if left in darkness 
too long, the rust is killed. 
Experiment 11. — In the preceding experiments, the plants were all 
placed in a dark moist chamber after spraying with the spore suspen- 
sion. Fromme (1915) and I (1915) have found that the germ-tubes of 
the uredospores of this rust are negatively helio tropic. It seems pos- 
sible from this that the retardation of the appearance of pustules 
might have been due to a failure of the germ-tubes to enter the host 
while in the dark. Then, when brought into the light, inoculation 
might have taken place from spores whose germination had been 
delayed. To test this a fourth experiment was set up in which some • 
of the plants, after being sprayed with the spore suspension, were left 
under bell jars in the light for from one to five days and were then 
placed under dark cylinders for various periods, after which some of 
them were returned to the light. After spraying with the spores, 
