primarily, is earth and air. This is
evident enough from the way in which they live. Many plants will
flourish in pure sand or powdered chalk, or on the bare face of a rock
or wall, watered merely with rain. And almost any plant may be made to
grow from the seed in moist sand, and increase its weight many times,
even if it will not come to perfection. Many naturally live suspended
from the branches of trees high in the air, and nourished by it alone,
never having any connection with the soil; and some which naturally grow
on the ground, like the Live-forever of the gardens, when pulled up by
the roots and hung in the air will often flourish the whole summer long.

447. It is true that fast-growing plants, or those which produce much
vegetable matter in one season (especially in such concentrated form as
to be useful as food for man or the higher animals) will come to
maturity only in an enriched soil. But what is a rich soil? One which
contains decomposing vegetable matter, or some decomposing animal
matter; that is, in either case, some decomposing organic matter
formerly produced by plants. Aided by this, grain-bearing and other
important vegetables will grow more rapidly and vigorously, and make a
greater amount of nourishing matter, than they could if left to do the
whole work at once from the beginning. So that in these cases also all
the organic or organizable matter was made by plants, and made out of
earth and air. Far the larger and most essential part was air and water.

448. Two kinds of material are taken in and used by plants; of which the
first, although more or less essential to perfect plant-growth, are in a
certain sense subsidiary, if not accidental, viz.:--

_Earthy constituents_, those which are left in the form of ashes when a
leaf or a stick of wood is burned in the open air. These consist of some
_potash_ (or _soda_ in a marine plant), some _silex_ (the same as
flint), and a little _lime_, _alumine_, or _magnesia_, _iron_ or
_manganese_, _sulphur_, _phosphorus_, etc.,--some or all of these in
variable and usually minute proportions. They are such materials as
happen to be dissolved, in small quantity, in the water taken up by the
roots; and when that is consumed by the plant, or flies off pure (as it
largely does) by exhalation, the earthy matter is left behind in the
cells,--just as it is left incrusting the sides of a teakettle in which
much hard water has been boiled. Naturally, therefore, the