1884] The Exhalation of Ozone by Flowering Plants. 473 
when the temperature did not mark over 70° Fahr. That the re- 
actions were not due to the nitrous oxides, perhaps the only 
remaining substances capable of producing like colorations of 
these test papers, will appear evident hereafter. 
It was next proposed to give foliage plants having soft thin 
leaves a trial. Seven asperdisteus, one fern and three dracænas 
were chosen for experimentation. These observations were con- 
ducted during the first week in September, 1883, for seven con- 
secutive days. The weather was extremely warm, the tempera- 
ture of the air within the case ranging from 85 to 100° Fahr., the 
sky was clear during four days and partly cloudy the remaining 
three. The Schoenbein test paper gave negative results through- 
out, while the guaiacum gave one “ very slight ” reaction, the 
rest being negative also. Thus it would appear that foliage 
plants have not this power of generating ozone, the function must 
therefore reside with the flower, but of its nature we shall speak 
hereafter, 
As our first experiments with inodorous flowering plants did 
not yield results striking enough to afford a basis for positive con- 
clusions, it was considered desirable to apply the tests to them in 
the open air, which was done. Seventeen thrifty geraniums were 
employed. The temperature was lower during these experiments 
than during those made indoors with inodorous plants. For six 
A secutive days, experiments being of ten hours each duration, the 
cenbein gave one negative, two “slight” and three “ marked” 
ia shades. The negative result occurred upon a rainy day, 
“nng which there was no sunshine whatever. This would indi- 
cate that sunlight, or at least good diffused light, is essential to 
Seneration of ozone by plants, for the plants were protected 
from the rain by the glass. There are other physiological pro- 
cesses carried on by plants which are almost entirely dependent 
ly the power of the sun's rays, 2. g., assimilation and transpi- 
ecu the above may doubtless be added the development 
io i ‘vations were continued upon these plants during the 
last Week of September, the result being about similar to those 
a sted, the Schoenbein gave two “marked,” one negative, on 
ty day, and the rest “ slight” reactions. The guaiacum 
As Snee: two “striking” and the rest “slight” colorations. 
Y intimated nitrous oxides, which are present in the air, 
