Autumn colours and the fall of the leaf.—As the summer wanes, the soil becomes colder, and the chilled roots lose much of their power of absorbing moisture. It is plain that if the leaves continued giving off water when no fresh supplies were forthcoming the tree would suffer. How is the danger to be met? Starch and other foods have already been stored up in quantity sufficient to supply the needs of the winter and the early spring. The leaves have finished their work, and one by one they fall off. But this does not take place until careful preparation has been made. Their green colouring matter breaks up; the part which may still be useful to the plant drains into the stem, leaving little heaps of yellow grains in the leaves. Or a special colouring matter may be formed, which, united in various ways with the materials of the dying leaf, gives the warm shades of red, orange, and purple which make the woods so beautiful in autumn. When all is ready, a layer of cork (Fig. 41, C) forms at the junction of the leaf stalk and the twig so that no raw wound may be left; the leaf-base splits across, just above the cork layer, and the leaf flutters to the ground, there to rot and make rich leaf mould. The leaf scars.—The former position of each leaf is now marked [Pg 60] by a curved scar (l.s. Fig. 34), and a row of brown dots (v.b.) in the scar still shows where the food-pipes bent outwards from the twig into the leaf. A line (a) stretches across and joins the two scars of each pair. The buds.—Just above every scar is the bud which arose in the axil of the fallen leaf. It is covered with overlapping scales of light green colour. At the end of the twig is a single terminal bud, similar in appearance to the axillary buds, but of larger size. It is instructive to take the terminal bud of a twig to pieces. The outer scales are tough and green, while the inner ones are thinner and have a beautiful silvery appearance. Usually there are fourteen scales. Each is long and narrow and bears at its upper end the rudiment of a leaf blade, which cannot usually be seen well without a lens. The scale is really a leaf which has been arrested in its development. Fig. 34.—Sycamore twig in winter. l.s., leaf-scars; v.b., ends of food-pipes; R, rings of scars left by scales of last winter’s terminal bud. (Slightly reduced.) Fig. 35.—Cross section of a Sycamore bud. (× 7.)