The Da Vinci Notebooks at sacred-texts.com
When the sun is in the East all the portions of plants lighted by it are of a most lively verdure, and this happens because the leaves lighted by the sun within the half of the horizon that is the Eastern half, are transparent; and within the Western semicircle the verdure is of a dull hue and the moist air is turbid and of the colour of grey ashes, not being transparent like that in the East, which is quite clear and all the more so in proportion as it is moister.
The shadows of the trees to the East cover a large portion of them and are darker in proportion as the foliage of the trees is thicker.