That part of a tree will show the fewest spaces, behind which a
large number of trees are standing between the tree and the air
[sky]; thus in the tree _a_ the spaces are not concealed nor in _b_,
as there is no tree behind. But in _c_ only half shows the spaces
filled up by the tree _d_, and part of the tree _d_ is filled up by
the tree _e_ and a little farther on all the spaces in the mass of
the trees are lost, and only that at the side remains.
451.