Vol. I: VIII. Botany for Painters and Elements of Landscape Painting: 442.
The Da Vinci Notebooks
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 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.