ngs may be considered as parts.

[Line in Organic Forms]

Look at any of the systems of line in the organic structures of nature:
the radiating ribs of the scallop shell, or the spiral of many other
varieties; the set of the feathers upon the expanded wing of a bird; the
radiation of the sun's rays; the flowing line of the wave movement; the
lines of structure in flowers and leaves; the scales of a fish; the
scales of a pine-cone or an artichoke. We feel that any of these
combinations of lines are harmonious and beautiful, and we know that
they are essential to the character and structure. They are organic
lines, in short. They mean life and growth. In principle they are
radiating and recurring lines; in each form they repeat each other in
varying degrees of direction and declension of curve. No two lines are
alike, yet there is no contradiction and no unnecessary line, and
variety is combined with unity. Each affords a perfect instance of
harmonious composition of line, and gives us definite principles upon
which to work (see illustration, p. 140[f080]).

[Illustration (f080): Principles of Structural and Ornamental Line in
Natural Forms.]

These systems of line in organic nature have been adopted and adapted by
art, and are found throughout the historical forms of ornament which, as
we have good reason to believe, were often derived from mechanical
structures, illustrating the same principles; which, again, the logic of
geometry enforces in drawing on plane surfaces.

All organic structures teach us the same lesson of relation and
recurrence of line. The bones of all vertebrate animals, from _fish_ to
_man_, illustrate the constant repetition in different degrees of the
same character and direction of line. The vertebral column itself is an
instance, and the recurring spring of the ribs from it, like the
branches from the stem of a tree, further expressed in the ramification
of the jointed bones of the limbs and extremities. The principle may be
followed out in the structure of the muscles in their radiating fibres,
which the delicate contours and flowing lines of the surface of the
body only combine in a greater degree of subtlety (see illustration, p.
142[f081a]).

[Illustration (f081a): Radiating, Recurring and Counterbalancing Lines
in the Structure of the Skeleton and the Muscles.]

Look at the anatomy of any tree, as it is disclosed to us in its wintry
l