72 
#05. The last author who has directed his attend 
lion to the effects produced in the air by living plants^ 
exposed to the direct influence of the solar rays, is 
M. T. de Saussure, in his elaborate treatise on 
vegetation, to which we have already so frequently 
referred. In many examples, however, atmospheric 
air does not seem to have experienced any ameliora- 
tion ; u hich accords with the observation of Senebier 
arid Woodhouse, that plants do not, even in sunshine, 
sensibly improve the atmosphere, unless it previously 
contain carbonic acid. M. de Saussure found, that 
three young peas, about 4 inches high, placed in 50 
cubic inches of pure atmospheric air, and exposed, 
from five to six hours a day, to the direct rays of the 
sun for ten days, in which time they increased in 
weight eight grains each, had not sensibly changed 
either the purity or volume of their atmosphere*. 
When the atmospheric air was previously washed in 
lime wafer, to free it from the carbonic acid naturally 
present in it, the same results were obtained* After 
fiv--' j or six days direct exposure to the sun, the air 
remained unchanged, both in purity and in volume, 
though the plants continued sound and vigorous in 
all their parts f. 
306 Similar results were afforded by plants of 
*ointa tumor-) -placed in 290 cubic inches of atmosphe- 
ric air, and, exposed, six hours a day, for six days, to 
tb-:- light of the sun ;- at the end of the experiment, 
the plants were found to have suffered no alteration, 
nor to have produced any change either in the purity 
* Recherches, p. 2^. o2. f ibid, p. 34. 35. 
