196 
E. B. MAINS 
the carbohydrates which had been formed while in the Hght. Follow- 
ing this, the plants were inoculated with uredospores of Puccinia 
Sorghi and placed in large-mouthed liter bottles. 
A carbon-dioxide-free atmosphere was obtained in these bottles 
by placing a strong solution of potassium hydroxide in the bottom of 
each and the oxygen supply was maintained by connecting the bottles 
with U tubes which contained a mixture of pumice-stone moistened 
with a KOH solution and pieces of KOH. Checks were run which 
were set up similarly, with the exception that KOH was omitted 
(Plate IV, figure i). All the joints and corks were coated with paraf- 
fine. 
Two experiments were conducted in this manner, the results of 
which are given below. 
Experiment 22. — In the first experiment, plants treated as above 
were inoculated and six (FC-E 60-65) were placed in bottles having 
a carbon-dioxide-free atmosphere and two (FC-E 66 and 67) in check 
bottles. The set was kept in the dark for 24 hours to allow the ap- 
paratus to become free from carbon dioxide and then was placed in 
the light of an east window at an average temperature of 22° C. In 
four days, numbers FC-E 60-65 began to show the effects of the lack 
of carbon dioxide by their sickly appearance. Numbers FC-E 66 
and 67 remained fresh and healthy. Pustules first showed on Num- 
bers FC-E 66 and 67 in eight days. The plants in carbon-dioxide-free 
atmosphere at this time showed no signs of infection. Numbers 
FC-E 64 and 65 were dead and the upper parts of the leaves of Num- 
bers FC-E 60-63 were also dead. 
The experiment was finished on the eleventh day. At this time 
no infection had taken place upon any of the plants in the carbon- 
dioxide-free atmosphere. 
Experiment 2j. — Eight plants (FC-E 68-75) which were treated 
as in the preceding experiment were inoculated with spores and placed 
under a dark cylinder for 12 hours at 18° C. Six of these (FC-E 68-73) 
were then placed in bottles with a carbon-dioxide-free atmosphere 
and two (FC-E 74, 75) were used as checks. The bottles were all 
kept in the dark for 12 hours so that the plants might not manufacture 
carbohydrates while containing carbon dioxide. Pustules appeared on 
both the checks in six days and on the seventh day pustules appeared 
on FC-E 69 and 73 in small numbers. These two plants, however, 
appeared fully as healthy in every way as the checks, while FC-E 
