lie scattered
dozens of tiny mouths or apertures, each of them guarded by two small
pursed-up lips which have a ridiculously human appearance when seen
through a simple microscope. When the conditions of air and moisture
are favourable, these lips open visible to admit gases; and then the
tiny mouths suck in carbonic acid in abundance from the air around
then. A series of pipes conveys the gaseous food thus supplied to the
upper surface of the leaf, where the sunlight falls full upon it. Now,
the cells of the leaf contain a peculiar green digestive material,
which I regret to say has no simpler or more cheerful name than
chlorophyll; and where the sunlight plays upon this mysterious
chlorophyll, it severs the oxygen from the carbon in the carbonic acid,
turns the free gas loose upon the atmosphere once more through the tiny
mouths, and retains the severed carbon intact in its own tissues. That
is the whole process of feeding in plants: they eat carbonic acid,
digest it in their leaves, get rid of the oxygen with which it was
formerly combined, and keep the carbon stored up for their own
purposes.

Life as a whole depends entirely upon this property of chlorophyll; for
every atom of organic matter in your body or mine was originally so
manufactured by sunlight in the leaves of some plant from which,
directly or indirectly, we derive it.

To be sure, in order to make up the various substances which compose
their tissues--to build up their wood, their leaves, their fruits,
their blossoms--plants require hydrogen, nitrogen, and even small
quantities of oxygen as well; but these various materials are
sufficiently supplied in the water which is taken up by the roots, and
they really contribute very little indeed to the bulk of the tree,
which consists for the most part of almost pure carbon. If you were to
take a thoroughly dry piece of wood, and then drive off from it by heat
these extraneous matters, you would find that the remainder, the pure
charcoal, formed the bulk of the weight, the rest being for the most
part very light and gaseous. Briefly put, plants are mostly carbon and
water, and the carbon which forms their solid part is extracted direct
from the air around them.

How does it come about then that a careless world in general, and more
especially the happy-go-lucky race of gardeners and farmers in
particular, who have to deal so much with plants in their practical
aspect, always attach so great importance to