Leaves Layered Like Ivy; the Leaves of the Walnut
Why leaves layer to catch dew, air, and sun, and the growth of the walnut's foliage
This all-text page of the sixth part of the Treatise on Painting explains why leaves turn upward to catch the slowly descending dew and why they are tiered on the plant so that one covers another as little as possible, like ivy on a wall: the layering leaves intervals for air and sun to pass and lets falling drops reach the leaves and boughs below. A chapter 'On the leaves of the walnut' follows, describing how the leaves crowd the year's twig, spacing wider and more numerous on younger branches, with fruit at the twig's tip and the heavier boughs hanging below because the sap tends to descend, and how leaves keep their underside turned toward the earth.
On this page
Leaves layered like ivy to admit air, sun, and dew
A leaf turns so its whole surface catches the dew that descends slowly from the air, and the leaves are tiered on the plant so one overlaps another as little as possible, as ivy does on a wall. This layering serves two ends: to leave intervals for air and sun to penetrate, and to let drops falling from one leaf reach the fourth and sixth leaves of the boughs below.
The leaves of the walnut: spacing, fruit, and growth
The walnut's leaves are spread along the year's twig, set wider apart and more numerous on younger branches, closer and fewer on older ones. The fruit grows at the twig's tip and the larger boughs hang below, since the sap descends more readily than it rises; twigs facing the sky spread their leaves evenly at the tip, those facing the horizon lie flat, and every leaf keeps its underside turned toward the earth.