124 Chapters in Modern Botany CHAP. 



was left to produce other sour plants, on which the snails, 

 this time a trifle less fastidious, have to begin anew. They 

 naturally select the sweeter, and hence " natural selection " 

 preserves and propagates the sourer ; and so on indefinitely, 

 and vegetation thus tends to grow sourer to all eternity. 

 For this the snails are responsible! Meanwhile, too, 

 natural selection, her ministers this time the browsing 

 mammals, is at work producing thorny plants, and so on. 

 It is the Darwinian theory in a nutshell ; and its accept- 

 ance or rejection is of fundamental importance to our 

 whole conception of evolution. Not only to Professor 

 Stahl, therefore, but to Mr. Wallace, to Professors Weis- 

 mann and Ray Lankester, perhaps even to the mildly 

 divergent Mr. Romanes, as assuredly to Sir John Lub- 

 bock or Mr. Grant Allen, such interpretations seem 

 not only valid but necessary, and not only necessary but 

 sufficient. 



You have two dozen apples in your fruit-basket just begin- 

 ning to spoil. Each day you take the two best, and at the 

 end of a week there are ten rotten apples left. To a slight 

 extent, it may be said, you are responsible for the growing 

 rottenness, for you might have periodically selected the 

 two worst, but the rottenness was there ; it not only arose, 

 but increased without you. Your selection, it is true, has 

 been such as to accelerate this disastrous evolution ; a 

 different selection would have retarded it ; what selection 

 can do then is at most to accelerate or slow the progress of 

 the selected along its definite grooves of natural change. 

 So the acids and ferments, the oils and encrustations, the 

 hurtful hairs and crystal needles, are constitutional peculi- 

 arities which arise in plants, and increase in them apart 

 altogether from any snails. Nature is indeed a marvellous 

 web, but we must not make it more tangled than it is. 

 The sourness, the poison, the ferments, the crystals, are, 



