The leaves of plants, being transparent, do not cast full darkness upon the leaves they shade; they send shadows of slight darkness that acquire a beauty of green. And the third leaves, lying beneath the first, take on a double darkness added to the darkness of the second leaf, because only two leaves shade them; and so the third, and then the fourth, keep multiplying in darkness, and would go on to infinity.

And therefore you, painter, when you make the masses of the great leafy boughs, make them more illuminated than the part toward the centre of the tree; and the masses of the branches nearer the light still more illuminated, and the masses of those masses more again, and the outermost leaves more, and most of all the outermost parts of the leaves turned toward the light.

All the grasses and leaves of the tree set between the eye and the sun are seen by transparency aided by the light of the sun, and this transparency is at its highest degree of beauty of green; and it comes more from the power of the sun's rays, which illuminate it from the opposite side, than from its own natural colour.

[891] On the shadows of transparent leaves.

The shadows that are on transparent leaves, seen from the reverse, are the very same shadows that are on the face of that leaf, and they show through from the reverse together with the luminous part; [but the sheen] can never show through. When one green mass is behind another, the sheens of the leaves and their transparencies appear of greater power than those which border on the brightness of the air. And if the sun illuminates the leaves without their coming between it and the eye, and without the eye itself seeing the sun, then the sheens of the leaves and their transparencies are excessive.