Although those leaves which have a polished surface are to a great
extent of the same colour on the right side and on the reverse, it
may happen that the side which is turned towards the atmosphere will
have something of the colour of the atmosphere; and it will seem to
have more of this colour of the atmosphere in proportion as the eye
is nearer to it and sees it more foreshortened. And, without
exception the shadows show as darker on the upper side than on the
lower, from the contrast offered by the high lights which limit the
shadows.

The under side of the leaf, although its colour may be in itself the
same as that of the upper side, shows a still finer colour--a colour
that is green verging on yellow--and this happens when the leaf is
placed between