197 
resin in plants, after having been brought out of a 
cellar, where they are almost white, and standing on- 
ly a couple of days exposed to the sun, makes this, 
says he, probable to me * ; and even Newton con- 
jectured, that gross bodies might receive much of 
their activity from the particles of light that entered 
into their composition f. Lastly, M. M. Chaptal 
and Hassenfratz found, that plants, which vegetated 
in darkness, contained much less carbon than those 
which had grown in the light ; and M. Senebier also 
ascertained, that such plants yielded less oil and re- 
sinous matter J ; facts which seem directly to prove 
the influence of light in increasing the proportion of 
combustible matter. 
469. But whence, it may be farther asked, is the 
alkali, which so much abounds in the ashes of the 
green parts of vegetables (377. ), and so directly con- 
tributes to their colour, derived ? It doubtless pre- 
exists in the vegetable body, and is not a product of 
combustion ; for it is found in combination with dif- 
ferent acids, and even in an uncombined state, before 
the process of combustion is instituted ; and that pro- 
cess, as M. Vauquelin has remarked, serves only to 
develope the saline matter, as the other constituents 
are consumed. How, then, does this matter gain ad- 
mission into the living plant ? It is probably held in 
solution in the fluids, which plants absorb from the > 
* On Air and Fire, p. 158. 
f Optics, Query 30. 
J Thomson's Chemistry, vol. v. p. 360. 4th edit. 
