RELATION OF SOME RUSTS TO THEIR HOSTS 
Others were kept in the dark for various periods of time and were then 
. brought into the light. 
Table III 
Effect of Light Upon the Development of Pnccinia Coronata. Comparison of Plants 
Inoculated in Light and in Darkness 
Pot No. 
Time in Light 
Time in Dark 
2d Period 
Time in Light 
Licubation 
Period 
Retardation 
c 17.19 
I day 
I " 
4 days 
4 " 
6 days 
6 " 
II days 
2 days 
C 17.20 
II " 
2 " 
C 17.21 
I " 
19+ " 
no infection 
C 17.22 
5 " 
15+ " 
c 17.23 
5 " 
6 " 
3 " 
14 days 
5 " 
c 17.24 
5 " 
6 " 
3 " 
14 " 
5 " 
c 17.25 
9 " 
9 " 
C 17.26 
9 " 
9 " 
c 17.27 
9 " 
9 " 
C 17.28 
5 " 
7 " 
12 " 
3 " 
C 17.29. .... 
I " 
8 " 
9 " 
c 17.30 
I " 
8 " 
9 " 
c 17.31 
5 " 
6 " 
II " 
2 " 
c 17.32 
20+ " 
no infection 
c 17.33 
I " 
8 " 
9 days 
C 17-34 
5 " 
7 " 
12 " 
3 " 
c 17.35 
II " 
10 " 
21 " 
12 " 
c 17.36 
5 " 
7 " 
12 " 
3 " 
Following this experiment, plants were inoculated in areas marked 
with India ink and covered with dark cylinders. After two days, the 
inoculated areas were sectioned and the sections treated with chloral 
hydrate and iodine. Mycelium was found in some of the inoculated 
areas, but had not developed to a very great extent. 
From these results it is evident that infection of Avena saliva by 
Puccinia coronata takes place in darkness as well as in light, although 
apparently the amount of infection is less in darkness. 
Puccinia Sorghi 
The first experiments upon the effect of light upon the development 
of Puccinia Sorghi were carried out in the same manner as with Puc- 
cinia coronata. The results obtained in these first experiments 
(Experiments 12-19) were not as clear cut as those obtained with the 
latter. Seven out of eleven plants which were in the dark three to 
eight days before being placed in the light had their incubation period 
lengthened one to two days. The other four had no retardation of 
their incubation period Four out of thirteen plants which were in 
