leaves, the
lateral ribs are set on their central rib is approximately the same at
which the branches leave the great stem; and thus each section of the
tree would present a kind of magnified view of its own leaf, were it not
for the interfering force of gravity on the masses of foliage. This
force in proportion to their age, and the lateral leverage upon them,
bears them downwards at the extremities, so that, as before noticed, the
lower the bough grows on the stem, the more it droops (Fig. 17, p.
295.); besides this, nearly all beautiful trees have a tendency to
divide into two or more principal masses, which give a prettier and more
complicated symmetry than if one stem ran all the way up the centre.
Fig. 41. may thus be considered the simplest type of tree radiation, as
opposed to leaf radiation. In this figure, however, all secondary
ramification is unrepresented, for the sake of simplicity; but if we
take one half of such a tree, and merely give two secondary branches to
each main branch (as represented in the general branch structure shown
at _b_, Fig. 18., p. 296), we shall have the form, Fig. 42. This I
consider the perfect general type of tree structure; and it is curiously
connected with certain forms of Greek, Byzantine, and Gothic
ornamentation, into the discussion of which, however, we must not enter
here. It will be observed, that both in Figs. 41. and 42. all the
branches so spring from the main stem as very nearly to suggest their
united radiation from the root R. This is by no means universally the
case; but if the branches do not bend towards a point in the root, they
at least converge to some point or other. In the examples in Fig. 43.,
the mathematical centre of curvature, _a_, is thus, in one case, on the
ground at some distance from the root, and in the other, near the top of
the tree. Half, only, of each tree is given, for the sake of clearness:
Fig. 44. gives both sides of another example, in which the origins of
curvature are below the root. As the positions of such points may be
varied without end, and as the arrangement of the lines is also farther
complicated by the fact of the boughs springing for the most part in a
spiral order round the tree, and at proportionate distances, the systems
of curvature which regulate the form of vegetation are quite infinite.
Infinite is a word easily said, and easily written, and people do not
always mean it when they say it; in this case I _do_ mean it; the n