8, The Rural Library. 



would take place if this individual or its adaptive offspring were to cross 

 with the main stock of the parent species ; for all the offspring of such a cross 

 which are intermediate in character and therefore less adapted to the new 

 conditions, would tend to disappear, and the two branches of the species 

 would, as a result, become more and more fixed and the tendency to cross 

 would constantly decrease. The refusal to cross, therefore, becomes a posi- 

 tive character of separation, and the "missing links" which result from 

 crossing are no more and no less inexplicable than the "missing links" due 

 to simple selection ; or, to put the case more accurately, natural selec- 

 tion Weeds out the tendency to promiscuous crossing when it is hurtful, un- 

 just the same manner that it it weeds out any other injurious tendency. It 

 makes no difference in what way this tendency expresses itself, whether in 

 some constitutional refusal to cross — if such exists — or in infertility of off- 

 spring, or in different times of blooming : all equally come under the same 

 power of natural selection. We are apt to look upon infertility as the ab- 

 sence of a character, a sort of a negative feature, which is somehow not the 

 legitimate property of natural selection ; but such is not the case. We are 

 perhaps led the more to this feeling because the word infertility is itself 

 negative, and because we associate full productiveness with the positive at- 

 tributes of plants. But loss of productiveness is surely no more a subject 

 of wonder than loss of color or size, if there is some corresponding gain to 

 be accomplished. In fact, we see in numerous plants which propagate easily 

 by means of runners and suckers, a very low degree of productiveness. 



Now, if this reasoning is sound, it leads us to conclusions quite the reverse of 

 those held by the advocates of the swamping effects of intercrossing, and 

 these conclusions are of the most vital importance to every man who tills 

 the soil. The logical result is simply this : the best results of crossing are 

 obtained, as a rule, when the cross is made between different individuals of 

 the same variety, or, at farthest, between different individuals of the same 

 species. In other words, hybrids — or crosses between species — are rarely 

 useful ; and it follows, as a logical result, that the more unlike the species, 

 the less useful will be the hybrids. This, I am aware, is counter to the 

 notions of most horticulturists, and, if true, must entirely overthrow our com- 

 mon thinking upon this subject. But I think that I shall be able to show that 

 observation and experiment lead to the same conclusion to which our philos- 

 ophy has brought us. 



At this point we must ask ourselves what we mean by "best results." I 

 take this phrase to refer to those plants which are best fitted to survive in 

 the struggle for existence — those which are most vigorous or most productive 

 or most hardy, or which possess any well-marked character or characters 

 which distinguish them in virility from their fellows. We commonly asso- 



