PROFESSOR VIRCHOW AND EVOLUTION. 387 



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 dif- 

 ferent shapes and forms. If other leaves, moreover, 

 were at hand endowed with similar forces, the attrac- 

 tion would extend to them a growth of the mass of 

 leaves being the consequence. 



We have strong reason for assuming that the ulti- 

 mate 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 lead, of necessity, to this 

 conception of molecular polarity. Under the opera- 

 tion 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 

 equilibrium, which there is an immediate effort to re- 

 store. The effort, incessantly defeated for the waves 

 continue to pour in is incessantly renewed; in the 

 molecular struggle matter is gathered from the soil and 

 from the atmosphere, and built, in obedience to the 



