ADDITIONS TO CHAP. II. 
OF THE CHANGES INDUCED ON THE AIH BY 
THE VEGETATION OF PLANTS. 
SECT. I. Of the Vegetation of Plants in tie Shade. 
222. JL HE necessity of water, heat, and air, to 
carry forward the process of vegetation, is universal- 
ly admitted, and the general operation of these agents 
is abundantly established by the facts (23. 4. 6.) al- 
ready related. In our former discussion of the spe- 
cific changes induced on the air by vegetation (29. 
et seq.), we endeavoured to establish, by experiment, 
the same general facts as have been described to take 
place in the germination of seeds ; but the facts, 
which are supposed to lead to an opposite conclusion, 
are so numerous, and, apparently, so decisive, as still 
to persuade many eminent chemists, that oxygen gas, 
instead of being consumed, is really produced by the 
ordinary process of vegetation. In the present chap- 
ter we propose, therefore, to reconsider our own ex- 
periments and opinions, and to examine, with more 
attention, those which are opposed to them, in order 
to discover, as far as we are able, the causes of these 
discordant results, and thus to arrive at as much truth 
B 
