SYSTEMS OF BREEDING 619 



crossed plants exceeds that of the self-fertilized by 22 per cent, whereas 

 there are only five species in which the mean of the mean heights of the 

 self -fertilized plants exceeds that of the crossed, and this only by 9 per cent. 1 



The writer again calls attention to the fact that while averages 

 are of prime consequence in commercial transactions, they do 

 not decide principles of breeding, and it is extremely suggestive 

 that even five species were decidedly more vigorous when inbred. 

 It determines definitely that there is nothing inherently and 

 necessarily evil in inbreeding, per se, for if such were the case it 

 would make itself evident in every instance. 



Speaking of the fertility of self -fertilized flowers, Darwin says, 2 

 " Their fertility ranges from zero to fertility equaling that of the 

 crossed flowers ; and of this fact no explanation can be offered." 

 Not only was this true, but the self -fertilized forms were some- 

 times actually more fertile than the crossed. 3 



This mystery, for which " no explanation can be offered," is 

 largely cleared up by our modern knowledge of heredity, as 

 is shown by what follows. 



The total effects of inbreeding. All characters, both good and 

 bad, exist in various degrees in different individuals. The prob- 

 lem in breeding is to secure the strongest combinations of desir- 

 able characters, and it is easy to show that this is accomplished 

 by inbreeding. Not only that, but it is also easy to show that 

 the same methods will secure the lowest attainable intensity, 

 a consummation desirable with unwelcome characters, and good 

 to know about as a general possibility. 



Take, for example, three intensities of any single character, 

 disregarding for the moment all questions of correlation. Let 

 these three intensities be represented by 3, 2, and I, respec- 

 tively, 2 being the mean. 



If, now, we exclude inbreeding, we find three unions possible, 

 -namely, 3 + 2, 3+1, and 2 + i ; but if we resort to inbreed- 

 ing, we make also the matings 3 + 3,2 + 2, i + I. Which unions 

 are richest in results ? In which have blood lines been most 

 intensified ? 



1 Darwin, Cross and Self Fertilization, etc., p. 283. 



2 Ibid. p. 326. 



3 Ibid. pp. 322-325. 



