work is done in or by means of them, a work upon which our own life depends
and that of all the living tribes around us.
Every leaf is a laboratory, in which, by the help of that great magician, the
sun, most wonderful changes and transformations are wrought. By the aid of the
sun the crude sap which is taken up from the ground is converted by the leaves
into a substance which goes to build up every part of the tree and causes it
to grow larger from year to year; so that instead of the tree making the leaves,
as we commonly think, the leaves really make the tree.
Leaves, like other parts of the plant or tree, are composed of cells and also
of woody material. The ribs and veins of the leaves are the woody part. By their
stiffness they keep the leaves spread out so that the sun can act upon them
fully, and they prevent them also from being broken and destroyed by the winds
as they otherwise would be. They serve also as ducts or conduits by which the
crude sap is conveyed to the leaves, and by whic
