and while, in certain circumstances, we admitted (45.) 
this production of oxygen, we denied (46.) that it 
either was or could be considered a necessary func- 
tion of vegetation. A more extended inquiry into 
the original facts, together with che additional light, 
which the late researches of M. de Saussure have 
afforded, have contributed to raise our view of the 
importance -of this subject ; and therefore, in the 
present section, we have submitted it to a fuller and 
more distinct discussion. 
281. On several occasions, we -have already al- 
luded to the operation of light in modifying the chan- 
ges which living vegetables produce in the air ; and 
we have also noticed the remarkable influence which 
it exerts in the production of the colours of plants. 
As we now propose to enter more fully into the na- 
ture of its operation on the vegetable kingdom, we 
shall briefly recite such additional facts and observa- 
tions, relating to its more general effects, as have 
since come to our knowledge. 
82. We before ascribed (25.) to M. du Fay the 
first observation respecting the direct agency of light 
in changing the colours of plants ; but a more ex- 
tended inquiry has taught us, that we must go much 
farther back to collect the first notices which relate 
to this subject. According to M. Senebier, Aristo- 
tje, in his theory of colours, remarks, that when wa- 
ter and the solar rays act together on plants, they 
produce a green colour ; and, in conjunction with 
earth, the same water produces whiteness. Hence 
all those parts of plants which lie beneath the soil, 
as roots and bulbs, appear white, while the parts. 
