CHAP. XII. 
DIGESTION. 
381 
experiments, that siliceous matter disappears in Corn, in pro- 
portion as care is taken to deprive the medium in which Corn 
grows of all access to siliceous solutions. He states that, upon a 
general review of his experiments, the results indicate decisively 
a connexion between the quantity of earthy matter contained in 
a plant, and the readiness with which the plant is supplied with 
such matter from without ; since, even if w'e confine ourselves 
to the examination of the parts above ground, where there can 
be no suspicion of any foreign admixture, it is found, as stated 
in the tables of experiments, that the largest amount of 
calcareous earth (for instance) was obtained from straw grown 
in Carrara marble; and so on. See, for some curious ex- 
periments on this subject, the Transactions of the Linncean 
Society, vol. xvii. p. 262. 
While, however, both experiment and theory disprove the 
formation of foreign matters by plants, it seems certain that 
silica and other earthy matters become, when they enter the 
tissue of a plant, organ isable products, occupying in some cases 
a definite and invariable position in the structure, as in Grasses. 
There are some good observations upon this subject in 
Taylor* s Magazine, vol. Ixvii. p. 414., by the Rev. J. B. Reade, 
who states that the skeletons of vegetable tissue remain after 
all the carbonaceous matter is removed ; and that both lime 
and potash enter as elements into’ the basis of vegetable tissue. 
He says he can prove that vessels are actually composed of 
silica, by showing that, if the latter is removed, no trace of 
vessel remains. 
It is not, however, a necessary inference from these data, 
that earthy matter is indispensable to vegetable organisation, 
partly because Dr. Daubeny’s experiments above referred to 
prove the contrary ; and, secondly, because Giippert has shown 
that mineral matter artificially introduced into plants will 
take entire possession of them, destroying or displacing the 
vegetable matter, without altering their tissue or their struc- 
ture. (Comptes rendiis, iii. 656.) Moreover, the old expe- 
riments of growing plants in pure water, where they are cut 
off from access to foreign matter, have been repeated by M. 
Boussingault and M. Colin [Comptes rendus, vii. 889. 949.); 
the former found that Peas, fed with nothing but air and 
