3§4 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
produced no bad effects on the occupants of the room so far as physiological 
and psychological tests show, and since Pettenkofer 5 long ago showed that 
carbon-dioxide is quite without effect on human beings in the highest con¬ 
centration that it ever attains in occupied rooms, our attention has been 
directed especially to the percentage of carbon-dioxide, during the day 
and night, in a room containing a large number of growing plants. 
The work was carried on in the greenhouse in Volunteer Park in Seattle. 
The room in which the samples of air for analysis were secured was well 
filled with plants, so that the total leaf area exposed was large in propor¬ 
tion to the volume of air. The investigation was carried on in July when 
the plants were growing actively. The room contained a considerable 
number of tropical plants whose growth was especially rapid and whose 
metabolism was thus very active. The plants were potted in rich soil 
fertilized with organic fertilizers every two weeks, and no doubt micro¬ 
organisms in the soil were active agents in the production of carbon-dioxide. 
The room had top ventilation of the type commonly provided in green¬ 
houses. 
Experimental 
Hesse’s method as reported by Scott 6 was utilized for determining the 
carbon-dioxide content of the air. The necessary apparatus together 
with the standard solutions were taken to the greenhouse, where all analyses 
were performed. This eliminated the transport of samples to the laboratory 
and facilitated the checking of data. The results were calculated for dry 
air at standard conditions and are reported in the number of parts of car¬ 
bon dioxide per ten thousand parts of air. 
All precautions were taken to keep reagents and samples of air col¬ 
lected from contamination by carbon-dioxide. The samples were secured 
by emptying a large Erlenmeyer flask, previously calibrated, of distilled 
water saturated with the air to be sampled and having the same tempera¬ 
ture. As soon as the flask was emptied, it was immediately corked and 
taken to the titration bench where standard barium hydroxide was added 
and the flask was shaken for ten or more minutes. The excess of alkali 
was titrated with standard oxalic acid, after washing down the sides of 
the flask with boiled distilled water. The solutions were admitted to the 
flask through a hole in the stopper of the flask. The data obtained are 
given in table I. 
Discussion 
It is evident that certain factors tend to decrease the amount of carbon- 
dioxide in the air of this greenhouse, while others tend to increase it. Under 
the first head come ( a ) the green plants which use carbon-dioxide in photo¬ 
synthesis during the day but not at night, and (b) ventilation, including 
5 Quoted by Winslow, loc. cit. 
6 Standard methods of chemical analysis, p. 728. 
