137 
loo, become green under a similar exposure to the 
solar rays. 
390. But although the light of the sun thus con- 
tributes to produce the green colour of plants, yet, 
as it operates chiefly by decomposing acid matter, and 
thereby reducing its predominance in the colourable 
juices of the leaf, it follows, that its agency is not es- 
sential to this production of colour, if the alkali, from 
any other cause, can be rendered predominant in 
those juices. Thus, when the colourless solutions of 
etiolated leaves, or the colourless infusions of flowers, 
are rendered green by alkalis, the agency of light is 
no way concerned in producing the effect ; and so, 
likewise, if the alkali, in living plants, can, in any 
way, be rendered predominant, under circumstances 
where light is excluded, still the colourable juices of 
the leaf may, nevertheless, be expected to exhibit 
more or less of a green colour. M. Senebier re- 
marks, that the leaves of etiolated French beans often 
exhibit a green appearance at the part where they 
are connected with the stalk ; and this appearance is 
seen at the commencement of vegetation, while the 
seed is yet buried in the earth, and before light, 
therefore, can have come into contact with it *. So, 
likewise, the buds of the chesnut, while enveloped 
in their thick and gummy cases, possess a green hue 
before their development ; whence, says he, it is not 
to be doubted, that vegetables, and parts of vegeta- 
bles, may be coloured green, although light does not 
seem to act immediately upon them ! 
* Mem, Pbys. torn, ii, p, 8& t Ibid P- 97* 
