Never paint leaves transparent to the sun, because they are confused; and this is because on the transparency of one leaf will be seen the shadow of another leaf which is above it. This shadow has a distinct outline and a certain depth of shade and sometimes is [as much as] half or a third of the leaf which is shaded; and consequently such an arrangement is very confused and the imitation of it should be avoided. 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. That tree will have the least shadow which has the fewest branches and few leaves. 433. OF DARK LEAVES IN FRONT OF TRANSPARENT ONES. When the leaves are interposed between the light and the eye, then that which is nearest to the eye will be the darkest, and the most distant will be the lightest, not being seen against the atmosphere; and this is seen in the leaves which are away from the centre of the tree, that is towards the light. [Footnote: See Pl. XXVIII, No. 2, the lower sketch.] 434. OF THE LIGHTS ON DARK LEAVES. The lights on such leaves which are darkest, will be most near to the colour of the atmosphere that is reflected in them. And the cause of this is that the light on the illuminated portion mingles with the dark hue to compose a blue colour; and this light is produced by the blueness of the atmosphere which is reflected in the smooth surface of these leaves and adds to the blue hue which this light usually produces when it falls on dark objects. OF THE LIGHTS ON LEAVES OF A YELLOWISH GREEN.