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.

But leaves of a green verging on yellow when they reflect the
atmosphere do not produce a reflection verging on blue, inasmuch as
every thing which appears in a mirror takes some colour from that
mirror, hence the blue of the atmosphere being reflected in the
yellow of the leaf appears green, because blue and yellow mixed
together make a very fine green colour, therefore the lustre of
light leaves verging on yellow will be greenish yellow.

A classification of trees according to their colours.

435.

The trees in a landscape are of various kinds of green, inasmuch as
some verge towards blackness, as firs, pines, cypresses, laurels,
box and the like. Some tend to yellow such as walnuts, and pears,
vines and verdure. Some are both yellowish and dark as chesnuts,
holm-oak. Some turn red in autumn as the service-tree, pomegranate,
vine, and cherry; and some are whitish as the willow, olive, reeds
and the like. Trees are of various forms ...

The proportions of light and shade in trees (436-440).

436.

OF A GENERALLY DISTRIBUTED LIGHT AS LIGHTING UP TREES.

That part of the trees will be seen to lie in the least dark shadow
which is farthest from the earth.

To prove it let _a p_ be the tree, _n b c_ the illuminated
hemisphere [the sky], the under portion of the tree faces the earth
_p c_, that is on the side _o_, and it faces a small part of the
hemisphere at _c d_. But the highest part of the convexity a faces
the greatest part of the hemisphere, that is _b c_. For this
reason--and because it does not face the darkness of the earth--it
is in fuller light. But if the tree has dense foliage, as the
laurel, arbutus, box or holm oak, it will be different; because,
although _a_ does not face the earth, it faces the dark [green] of
the leaves cut up by many shadows, and this darkness is reflected
onto the under sides of the leaves immediately above. Thus these
trees have their darkest shadows nearest to the middle of the tree.

437.

OF THE SHADOWS OF VERDURE.


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