198 
situations in which they grow. Thus, it is known, 
that terrestrial plants afford potassa, while those 
which grow in, and near the sea, chiefly furnish soda ; 
but M. M. du Hamel and Cadet found, that, if ma- 
rine plants be removed to in.land situations, they gra- 
dually cease to yield soda, and at length potassa on- 
ly is obtained * ; - facts which prove the influence of 
situation, in determining the kind and quantity of al- 
kaline matter. 
470. From the recent investigations of Mr Davy, 
we learn, also, that almost all solids and fluids, even 
the purest distilled water, contain saline matter ; so 
that nearly every substance which enters vegetables 
must convey to them a portion of it. It cannot, 
however, be supposed, that the alkali is formed in 
the vegetable directly from its proper elements ; for 
the bases of the alkalis so rapidly abstract oxygen 
from almost every other substance, that they cannot, 
as Mr Davy remarks, exist near the surface of the 
earth in a pure form. And farther, as the alkalis 
themselves attract acids, with scarcely less avidity 
than their bases attract oxygen, the same reasoning 
obliges us to suppose, that, as pure alkalis, these sub- 
stances do not enter plants ; wherefore we must 
conclude, that they chiefly gain admission, in combi- 
nation with different acids, that is, in a neutro-saline 
state f. 
471. After their entrance into vegetables, these 
saline bodies may be presumed to undergo various 
* Murray's Chemistry, vol. li. p. 94., 95. 
t Phil, Trans. 1807. 
