to do so--a power external to themselves, or
an inherent force? Science rejects the outside builder; let us,
therefore, consider from the other point of view the experience of the
present year. A low temperature had kept back for weeks the life of
the vegetable world. But at length the sun gained power--or, rather,
the cloud-screen which our atmosphere had drawn between him and us was
removed--and life immediately kindled under his warmth. But what is
life, and how can solar light and heat thus affect it? Near our elm
was a silver birch, with its leaves rapidly quivering in the morning
air. We had here motion, but not the motion of life. Each leaf moved
as a mass under the influence of an outside force, while the motion of
life was inherent and molecular. How are we to figure this molecular
motion--the forces which it implies, and the results which flow from
them? Suppose the leaves to be shaken from the tree and enabled to
attract and repel each other. To fix the ideas, suppose the point of
each leaf to repel all the other points and to attract the roots, and
the root of each leaf to repel all other roots, but to attract the
points. The leaves would then resemble an assemblage of little
magnets abandoned freely to the interaction of their own forces. In
obedience to these they would arrange themselves, and finally assume
positions of rest, forming a coherent mass. Let us suppose the
breeze, which now causes them to quiver, to disturb the assumed
equilibrium. As often as disturbed there would be a constant effort
on the part of the leaves to re-establish it; and in making this
effort the mass of leaves would pass through different shapes and
forms. If other leaves, moreover, were at hand endowed with similar
forces, the attraction would extend to them--a growth of the mass of
leaves being the consequence.

We have strong reason for assuming that the ultimate particles of
matter--the atoms and molecules of which it is made up--are endowed
with forces coarsely typified by those here ascribed to the leaves.
The phenomena of crystallisation load, of necessity, to this
conception of molecular polarity. Under the operation of such forces
the molecules of a seed, like our fallen leaves in the first instance,
take up positions from which they would never move if undisturbed by
an external impulse. But solar light and heat, which come to us as
waves through space, are the great agents of molecular disturbance. O