RELATION OF SOME RUSTS TO THEIR HOSTS 
Table IV 
Effect of Light Upon Development of Puccinia Sorghi. Plants Exhausted as Nearly as 
Possible of Soluble Carbohydrates 
Plant No. 
Age of 
Plant 
Endosperm 
Time iu Dark 
Time in Light 
Incubation 
Period 
Retard- 
ation 
FC-E 50.... 
13 days 
without 
5 days 
(died) 
no infection 
FC-E 51.... 
13 " 
7 days 
7 days 
7 " 
FC-E 52.... 
13 " 
7 " 
FC-E 55.... 
13 " 
8 " 
8 " 
FC-E 54-. ■• 
13 " 
3 days 
3 " 
7 " 
10 " 
3 d^ys 
2 " 
FC-E 58.... 
13 " 
6 " 
9 " 
FC-E 59.... 
13 " 
3 " 
7 " 
10 " 
3 " 
FC-E 56.... 
13 " 
6 " 
7 " 
no infection 
(died) 
FC-E 60.... 
13 " 
6 " 
6 days 
12 days 
5 " 
FC-E 61.... 
13 " 
6 " 
(died) 
no infection 
FC-E 53.... 
13 " 
10 days 
13 " 
FC-E 57.... 
13 " 
of the host, but the apparent exceptions in the previous experiments 
due to the presence of reserve food in the host only strengthen this 
conclusion the more. 
Effect of the Lack of Carbon Dioxide upon Development 
The preliminary experiments to show the effect of the lack of 
carbon dioxide upon development were not satisfactory, since the 
plants used possessed an endosperm and derived their food supply 
from it as was shown by the plants in a minus carbon dioxide atmos- 
phere developing as well as those of the check. Infection occurred at 
the same time as in the checks or a few days later. Since the experi- 
ments with light, which were being run at the same time, pointed to 
carbohydrates as factors in the development of the rusts, it was evident 
that the plant must be deprived as nearly as possible of carbohydrates. 
This was attempted in two experiments. 
Maize was germinated in a moist chamber at 30° C. and at the end 
of six days, when the plumule had reached the length of five to six 
centimeters, the endosperm was dissected away and the plants were 
planted in small bottles filled with quartz sand and moistened with 
Knop's solution. The plants were grown in the light for a few days 
until the leaves were expanded and chlorophyll had developed. They 
were then placed in a dark chamber for three days to exhaust them of 
