_Fig_21.jpg)
Fig. 21.—A portion of the ultimate
ramifications of the vascular bundles,
showing tracheids only, isolated from
the leaf by maceration.
When young, the leaves are red, gradually becoming a bright apple-green, and finally—in the autumn—becoming russet-brown in color. Young oaks retain their dead leaves till far into the winter, and even old trees usually have some leaves attached till January. The young leaves secrete small quantities of sweet liquid on the superior face of the lamina, and are much visited by bees and wasps; this honey must come through the membrane. As the leaves approach maturity the lamina becomes bright and hard.
The arrangement of the leaves is expressed by the fraction two fifths, as already described, each node giving off one leaf at an open angle, the points of insertion being so arranged that a line drawn from the insertion of a given lower leaf, and joining it to the points of insertion of those above, passes twice round the twig before we arrive at the leaf situated vertically above the one started from, and this upper leaf is the sixth above. Although this is the commonest and normal arrange-
