How Plants Perpetuate Their Kinds 293 



tions wholly needless in the asexual methods. Yet plants can 

 reproduce perfectly well by the direct and simple asexual methods. 

 In what, then, consists the superiority of sexual reproduction that 

 plants and animals should not only take so great trouble to secure 

 it, but should even abandon in the higher forms the asexual 

 method entirely? Many answers have been proposed for this 

 question, and we do not yet know the truth with certainty; but 

 the most probable explanation is derived from the fact that sex- 

 ually produced individuals are usually more variable, adaptable, 

 and vigorous than those asexually produced, and hence in the 

 long run overcome the latter in the struggle for existence, and sur- 

 vive while the others die out. An asexually generated individual 

 is naturally no more than a chip of the old block, and can differ 

 but little therefrom, while one sexually produced has the possi- 

 bility of combining the good qualities from two parents. Now if 

 conditions surrounding plants were unchanging, and all plants 

 were adapted the best possible thereto, then the asexual method 

 might be really the better; but the conditions of the world are 

 continually changing, and therefore those animals and plants 

 which possess the most variability and adaptability have the 

 best chance of maintaining themselves therein. This is the reason, 

 I think, why sexual reproduction, despite its complications, has 

 displaced the far simpler asexual kind. 



The greater constancy of characteristics usually distinctive of 

 asexual reproduction, in comparison with the greater variability 

 associated with the sexual type, has some very practical conse- 

 quences. Thus, as everybody knows, we can reproduce Bartlett 

 pear trees by the asexual method of grafting, and keep the fine 

 qualities of the fruit; but if we propagate them by seeds, which 

 of course are formed only as a result of fertilization, we do not get 

 Bartlett pears at all, but just a plain mongrel variety; and the 

 same thing is true of many other kinds of highly perfected garden 

 plants. This principle is so well understood by gardeners that 

 whenever they seek to secure new forms of plants, they make use 



