PROFESSOR VIRCHOW AND EVOLUTION. 389 



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 crystallisaUoa. 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 equilibrium, which there is an immediate effort 

 to restore. 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 



