of the Permanence of Varieties. 197 



propagated forms, one that probably Knight never thouglit of, 

 but wliich we should not liave expected recent writers to 

 overlook. When Mr. Darwin announced the principle that 

 cross-fertilization between the individuals of a species is the 

 plan of nature, and is practically so universal that it fairly 

 sustains Iiis inference that no hermaphrodite species continu- 

 ally self-fertilized would continue to exist, he made it clear to all 

 Avho apj)rehend and receive the principle, that a series of plants 

 propagated by buds only must have weaker hold of life than 

 a series reproduced by seed. For the former is the closest 

 possible kind of close breeding. Upon this ground such 

 varieties may be expected ultimately to die out ; but " the 

 mills of the gods grind so exceedingly slow," that we cannot 

 say that any particular grist has been actually ground out 

 under human observation. 



If it be asked how the asserted principle is proved or made 

 probable, we can here merely say that the proof is wholly infe- 

 rential. But the inference is drawn from such a vast array of 

 facts that it is well nigh irresistible. It is the legitimate expla- 

 nation of those arrangements m nature to secure cross-fertiliza- 

 tion in the species, either constantly or occasionally, which are 

 so general, so varied and diverse, and, we may add, so exquisite 

 and wonderful, that, once propounded, we see that it must be 

 true. What else, indeed, is the meaning and use of sexual 

 reproduction ? Not simply increase in numbers ; for that is 

 otherwise effectually provided for by budding propagation in 

 plants and many of the lower animals. There are plants, 

 indeed, of the lower sort, in which the whole multiplication 

 takes place in this way, and with great rapidity. These also have 

 sexual reproduction ; but in it two old individuals are always 

 destroyed to make a single new one ! Here propagation 

 diminishes the number of individuals 50 per cent. Who can 

 suppose that such a costly process as this, and that all the 

 exquisite arrangements for cross-fertilization in hermaphrodite 

 plants, do not subserve some most important purpose ? How 

 and why the union of two organisms, or generally of two very 

 minute portions of them, should reenforce vitality, we do not 

 know and can hardly conjecture. But this must be the mean- 

 ing of sexual reproduction. 



The conclusion of the matter from the scientific point of view 

 is, that sexually propagated varieties, or races, altliough liable 

 to disappear through change, need not be expected to wear 

 out, and there is no proof that they do — but that non-sexually 

 propagated varieties, though not liable to change, may theo- 

 retically be expected to wear out, but to be a very long time 

 about it. 



Ann. <£' Mag. N. Hist. Ser. 4. VoJ. xv. 14 



