¢ 4) 
drydrogen is the principal constituent; and that 
though there is nothing in the present ‘state of our 
experience that directly establishes this doctrine, 
yet that iis truth ought to be presumed, from the 
analysis of plants and the necessary and well known 
action of water on vegetation.” 
Ill. Of atr, and its agency in vegetation : 
A seed deprived of air will not germinate ; and a 
plant placed under an exhausted receiver, will soon 
perish. Even in a close and badly ventilated gar- 
den, vegetables indicate their situation; they are 
sickly in appearance, and vapid in taste. These 
facts sufficiently shew the general utility of air to 
vegetation: but this air is not now the simple and 
elementary body, that the ancient chemists describ- 
ed it to be. Priestly first, (1) and Lavoisier after 
him, analysed it, and found, that when pure, it con- 
sisted of about 70 parts of azote, 27 of oxigen, and 
2 of carbonic acid. In its ordinary (or impure) 
state, it is loaded with foreign and light bodies; 
such as mineral, animal and vegetable vapors, the 
seeds of plants and the eggs of insects, &c. Is it to 
this aggregate, that vegetation owes the services 
rendered to it by air? And if not, to how many, and 
to which, of its regular constituents, are we to as- 
cribe them? This enquiry will form the subject of 
the present article. 
All vegetables in a state of decomposition, give 
azole ; and some of them [cabbages, radishes, &c.] 
give itin great quantity. This abundance, combin- 
. (1) See Priestly’s Experiments and Observations on different kinds of Air, begua 
in 1767. 
6 
