526 
FOODS OF PLANTS. 
earths of that kind exist; as much as 65 per cent, of lime 
has been found in plants, of which substance no traces could 
be found in the ground ; and silica also, though none existed 
where the plants grew. 
It has been found, by experiment, that plants do not 
absorb solutions of saline substances indiscriminately; it 
may depend more on the degree of liquidity than on any 
discriminating power in the root; but we are wholly unable 
to explain that so much a greater portion of water should be 
absorbed than of the salt held in solution. Saussure con¬ 
cluded that it does not so much depend on the earths which 
constitute the soil, as on the quantity of earths held in solu¬ 
tion by the liquid part of it. So that earthy and saline 
matters existing in the soil, and being always found in 
plants, we can scarcely help considering them as a substance 
necessary to the growth of plants ; but without manures, no 
earths, salts, air, or water will support their proper growth. 
Giobert mixed four earths—silica, alumina, lime, and mag¬ 
nesia—in proportions to constitute a fertile soil, and supplied 
the plants growing in them with water; but none grew till 
he applied water from a dung-hill. Lampadius planted 
vegetables in one pure earth, and supplied them with 
dung-hill water; they grew and contained the usual earthy 
matters, notwithstanding the total absence of any of them 
in the soil. Plants have been resolved by chemical ana¬ 
lysis, but no satisfactory conclusions as to what sub¬ 
stances they derive from the earth as nourishment can be 
drawn from a knowledge of the constituent parts of organi¬ 
zation. If a plant be strongly heated in a close vessel, 
allowing only smoke to escape, the residue is always the 
same, and is called charcoal or carbon by the chemists; of 
this carbonaceous matter a considerable quantity is always 
found in garden-moulds and in rich lands, derived no doubt 
from the remains of vegetable substances of which the 
mould was originally formed. It is insoluble in water, and 
cannot enter in that state into plants; hence we may sup¬ 
pose that it is rendered acceptable to their pores by a variety 
of changes and combinations.— Farmer's Magazine . 
(To be continued .) 
