OF THE HERBS OF THE FIELD.
Of the plants which take a shadow from the plants which spring among them, those which are on this side [in front] of the shadow have the stems lighted up on a background of shadow, and the plants on which the shadows fall have their stems dark on a light background; that is on the background beyond the shadow.
OF TREES WHICH ARE BETWEEN THE EYE AND THE LIGHT.
Of the trees which are between the eye and the light the part in front will be light; but this light will be broken by the ramifications of transparent leaves—being seen from the under side—and lustrous leaves—being seen from the upper side; and the background below and behind will be dark green, being in shadow from the front portion of the said tree. This occurs in trees placed above the eye.
Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.