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SECT. IV. Of the Physical and, Chemical Agency oj Light > 
in promoting the Colouration of Plants. 
411. So far we have spoken of the colours of plants, 
as arising from variations in their chemical constitution 
alone ; and these variations we have attributed to the 
decomposition of their saline compounds, by the agen- 
cy of solar light. We have next to inquire into the 
manner in which light exerts this action, a subject of 
very nice and difficult investigation, but the impor- 
tance of which will, we hope, furnish an apology for 
the apparent temerity of our attempt, even although 
we should fail in its execution; 
412. Besides this chemical action, which light has 
been shewn to exert, we have also to consider its 
property of imparting colour ; for when it has been 
said that the predominance of acid or alkaline mat- 
ter renders the vegetable juices red or green, it 
must be understood to mean only, that such a state 
or constitution of those juices is thereby induced, as, 
in the language of Sir Isaac Newton, enables them, 
more or less, to reflect or transmit the red, or green, 
making rays of light. We do not, however, propose 
to go far into the consideration of these subjects, but 
to select and exhibit such facts only, as force them- 
selves on our notice, by the near connection which 
they seem to have with the more immediate objects 
of our research, 
