built up. Perhaps I may be excused for noting a sample of these early speculations, already possibly known to a few of my readers, but which here finds a more suitable place than that which it formerly occupied.
Sitting, in the summer of 1855, with my friend Dr. Debus under the shadow of a massive elm on the bank of a river in Normandy, the current of our thoughts and conversation was substantially this: We regarded the tree above us. In opposition to gravity its molecules had ascended, diverged into branches, and budded into innumerable leaves. What caused them 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 birch-tree and enabled to attract and repel each other. To fix the ideas, suppose the point of each leaf to repel all other points and to attract the other ends, 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 reestablish 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 action 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 crystallization lead, 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. On the inert molecules of seed and soil these waves impinge, disturbing the atomic
