The light shines least through a leaf when it falls upon it at an acute angle.
The gradations of shade and colour in leaves (430-434).
430
The shadows of plants are never black, for where the atmosphere penetrates there can never be utter darkness.
431
If the light comes from m and the eye is at n the eye will see the colour of the leaves a b all affected by the colour of m —that is of the atmosphere; and b c will be seen from the under side as transparent, with a beautiful green colour verging on yellow.
If m is the luminous body lighting up the leaf s all the eyes that see the under side of this leaf will see it of a beautiful light green, being transparent.
In very many cases the positions of the leaves will be without shadow [or in full light], and their under side will be transparent and the right side lustrous [reflecting light].
432
The willow and other similar trees, which have their boughs lopped every 3 or 4 years, put forth very straight branches, and their shadow is about the middle where these boughs spring; and towards the extreme ends they cast but little shade from having small leaves and few and slender branches. Hence the boughs which rise towards the sky will have but little shade and little relief; and the branches which are at an angle from the horizon, downwards, spring from the dark part of the shadow and grow thinner by degrees up to their ends, and these will be in strong relief, being in gradations of light against a background of shadow.