386 
AMERICAN JOURNAL OF BOTANY 
[Vol. io. 
tended to decrease it. There seems to be no reason to suppose that ven¬ 
tilation was more effective in decreasing carbon-dioxide content at night 
than during the day. 
The only remaining cause that could account for the accumulation of 
carbon-dioxide in the daytime was the presence of people visiting the 
greenhouse. The number of visitors varied greatly on different days and 
at different times of the day. A very high percentage of carbon-dioxide 
was found at one time when a gathering of florists and botanists inspected 
the greenhouse and it was crowded during the entire afternoon, and also 
on another occasion when a large number of school children came to see 
the plants. The irregularity in the number of visitors is undoubtedly the 
cause of the wide discrepancies in the values found at different times. The 
greenhouse was closed to visitors at 6 P.M. 
Since, according to Winslow’s data, the amount of carbon-dioxide 
could be increased to a point five to fifteen times as great as the maximum 
found in this greenhouse without injury to people, and since the amount 
of leaf area exposed here was very large in proportion to the volume of the 
air, while it is very small where a few plants are kept in sleeping rooms, 
it would seem that the amount of carbon-dioxide produced by a few plants 
in a sleeping room would not reach the danger point for the occupants 
or even approach it. Any danger must rest on other grounds, such as 
high temperature, high moisture content of the air, or some other factor. 
Summary 
1. Determinations of the carbon-dioxide content of the air in a green¬ 
house indicate that the concentration of this gas did not at the time of 
any determination reach a high enough concentration to be injurious to 
human beings. 
2. Under the conditions existing in this greenhouse, the effect of plants 
in increasing carbon-dioxide content is negligible in comparison with the 
effects of the people who visit the greenhouse. 
3. Any bad effects that may at any time have been experienced from 
the presence of plants in reasonably ventilated sleeping rooms must rest 
on some other basis than carbon-dioxide production. 
The authors wish to acknowledge the courtesies extended to them dur¬ 
ing this investigation by the Park Board of the City of Seattle. 
