changes ; for, both in terrestrial and marine plants, 
alkaline matter is found in combination with different 
vegetable and mineral acids. Hence, therefore, we may 
reasonably suppose, that these saline compounds are 
decomposed, and formed anew, at different periods ; 
and the great quantity of alkali that exists in the 
leaves, its presence in an uncombined state, and the 
chemical agency of light to which it is there exposed, 
all concur to shew, that these changes are principally 
" effected in those organs. By such decompositions, 
alkaline matter may be developed, even although no 
oxygen gas be afforded, since the acid that is separ 
rated may not be decomposed ; and thus light, by its 
chemical agency, may contribute to produce the 
green colour in plants, not merely by decomposing 
carbonic acid, in the manner already described, but 
by acting on such other saline compounds as may 
be present in the vegetable fluids. 
472. These views, respecting the entrance of saline 
matter into plants, and its subsequent decomposition, 
derive support from some well-established facts, re- 
lating to the use of lime in the practice of agricul- 
ture. The good effects of this substance, when laid 
upon soils, endure only for a limited period ; and 
hence its application is usually repeated every ten or 
twelve years. In some soils, the lime may, perhaps, 
act mechanically in improving the texture ; in others, 
it may act act chemically, both in improving the texr 
ture, and in facilitating the decomposition of organic 
matters ; but it may also, we believe, act physiologi- 
cally on the plant itself, by mixing with its fluids, and 
serving those useful purposes in the vegetable econo- 
