for ever this strange illusion--if people
ever thought; but of course they don't think--I mean Other People. The
true mouths and stomachs of plants are not to be found in the roots,
but in the green leaves; their true food is not sucked up from the
soil, but is inhaled through tiny channels from the air; the mass of
their material is carbon, as we can all see visibly to the naked eye
when a log of wood is reduced to charcoal: and that carbon the leaves
themselves drink in, by a thousand small green mouths, from the
atmosphere around them.

But how about the juice, the sap, the qualities of the soil, the manure
required? is the incredulous cry of Other People. What is the use of
the roots, and especially of the rootlets, if they are not the mouths
and supply-tubes of the plants? Well, I plainly perceive I can get 'no
forrarder,' like the farmer with his claret, till I've answered that
question, provisionally at least; so I will say here at once, without
further ado--the plant requires drink as well as food, and the roots
are the mouths that supply it with water. They also suck up a few other
things as well, which are necessary indeed, but far from forming the
bulk of the nutriment. Many plants, however, don't need any roots at
all, while none can get on without leaves as mouths and stomachs. That
is to say, no true plantlike plants, for some parasitic plants are
practically, to all intents and purposes, animals. To put it briefly,
every plant has one set of aerial mouths to suck in carbon, and many
plants have another set of subterranean mouths as well, to suck up
water and mineral constituents.

Have you ever grown mustard and cress in the window on a piece of
flannel? If so, that's a capital practical example of the comparative
unimportance of soil, except as a means of supplying moisture. You put
your flannel in a soup-plate by the dining-room window; you keep it
well wet, and you lay the seeds of the cress on top of it. The young
plants, being supplied with water by their roots, and with carbon by
the air around, have all the little they need below, and grow and
thrive in these conditions wonderfully. But if you were to cover them
up with an air-tight glass case, so as to exclude fresh air, they'd
shrivel up at once for want of carbon, which is their solid food, as
water is their liquid.

The way the plant really eats is little known to gardeners, but very
interesting. All over the lower surface of the green leaf