214 INBREEDING AND OUTBREEDING 



who has achieved quite a remarkable success with Berk- 

 shires, rarely went outside of his own drove for breeding 

 stock. He is quoted as saying (Mumford 158 ) : "If it is 

 true that inbreeding intensifies weakness of constitution, 

 lack of vigor, or too great fineness of bone, as we all be- 

 lieve, is it not as reasonable and as certain that you can 

 intensify strength of constitution, heavy bones, or vigor, 

 if you have these traits well developed in the blood of the 

 animals you are inbreeding? I think I have continued to 

 improve my herd, being now able to produce a larger per- 

 centage of really superior animals than at any time in 

 the past." 



This quotation exemplifies the opinion of the best in- 

 formed of the practical breeders of the present day in re- 

 gard to the practice of inbreeding. In general they recog- 

 nize that the results obtained depend largely upon the 

 character and constitution of the animals, and the care 

 and skill with which they are selected for mating. They 

 have learned by experience what matings are the most 

 successful and how far it is advisable to carry close breed- 

 ing with a particular stock. Rarely is inbreeding as close 

 as brother and sister or parent and offspring mating con- 

 tinued for many successive generations, however ; for they 

 are apprehensive at all times that inbreeding may reduce 

 the fertility and lessen the constitutional vigor of their 

 animals, and they frequently introduce stock from outside 

 to counteract any tendency in this direction whether 

 fancied or real. 



In plants the problem is different. No systematic in- 

 dividual mating system is practiced, as is the case with 

 animals, so that whether plants are inbred or outbred is a 

 matter which is left to regulate itself automatically. 



