The Walnut: Leaf Distribution and the Weight of Sap
Why the largest branches hang low and slender ones climb toward the sky
Illustrated by a drawn walnut spray and separate twig studies, Leonardo sets out the growth laws of the walnut. Leaves are spaced farther apart and more numerous on younger branches, closer and fewer on older ones, while the fruit forms at the twig's tip. He reasons that the larger branches sit below because the weight of the sap descends more easily than it rises, leaving the upward branches thin; and he notes that a twig facing the sky spreads its leaves evenly by their tips, whereas one facing the horizon lies flat, since leaves keep their undersides turned toward the earth.
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Leaf spacing, fruiting tips, and sap that sinks
Walnut leaves are more distant and more numerous the younger the branch, closer and fewer the older it is, with fruit born at the twig's extremity. The larger branches lie below because the weight of the sap descends more readily than it rises, so the upward branches stay small and slender; a twig facing the sky spreads its leaves by their tips, while one facing the horizon lies flat, the leaves keeping their underside toward the earth.
Twigs shrink nearer the branch that bears them
The separate twig studies illustrate the rule that a twig is the smaller the nearer it is born to the origin of the branch that produces it.