§ 1. Having now some clear idea of the position of the bud, we have next to examine the forms and structure of its shield—the leaf which guards it. You will form the best general idea of the flattened leaf of shield-builders by thinking of it as you would of a mast and sail. More consistently with our classification, we might perhaps say, by thinking always of the arm sustaining the shield; but we should be in danger of carrying fancy too far, and the likeness of mast and sail is closer, for the mast tapers as the leaf-rib does, while the hand holding the uppermost strap of the buckler clenches itself. Whichever figure we use, it will cure us of the bad habit of imagining a leaf composed of a short stalk with a broad expansion at the end of it. Whereas we should always think of the stalk as running right up the leaf to its point, and carrying the expanded, or foliate part, as the mast of a lugger does its sail. To some extent, indeed, it has yards also, ribs branching from the innermost one; only the yards of the leaf will not run up and down, which is one essential function of a sailyard.

§ 2. The analogy will, however, serve one step more. As the sail must be on one side of the mast, so the expansion of a leaf is on one side of its central rib, or of its system of ribs.