92 
329. According to Dr Ingenhousz, plants, inclo- 
sed in iacw> 5 continually give out air, which in sun- 
shine is oxygen gas, and in the shade is carbonic 
acid and nitrogen. The air contained in onions and 
in many aquatic plants he represents to be nearly 
the same as that which surrounds them. In tubes 
filled with nitrogen, the gas afforded by rushes was 
of the same quality ; and when the tubes were filled 
with oxygen, the plants afforded gas of the same de- 
gree of purity. Similar results wen.- obtained when 
the tubes were filled with hydrogen or carbonic acid 
gases, the air afforded being in every case similar to 
that which previously surrounded the plants. The 
experiments succeeded in sunshine and in the shade, 
and the change in the quality of the air was effected 
in half an hour ; so that it is concluded, that the air 
existing in plants is never stagnant, but is constantly 
and speedily renewed *. 
330. M. Senebier ascertained, by experiment, the 
truth of the foregoing observations, as far as they 
relate to plants which have a reservoir for air, such 
as the stems of onions and rushes ; but that they do 
not hold with regard to plants of a different struc- 
ture. The air which generally issued first from 
plants in vaciw he found to be nearly similar to that 
of the atmosphere, but it diminished in purity as the 
experiment was prolonged. It varied, however, in 
the same plants, at different times ; and contained 
different proportions of oxygen, carbonic acid, and 
nitrogen gases f. 
* Exper. t. ii. p. 90. 99. 
t Physiol. Veg. t, iii. p. 120. et seq. 
