464 GENERAL RESULTS. CHAP. XII 



observation, have acted on this principle, and have kept 

 stocks of the same animals at two or more distant and 

 differently situated farms. They have then coupled 

 the individuals from these farms with excellent results.* 

 This same plan is also unconsciously followed whenever 

 the males, reared in one place, are let out for propaga- 

 tion to breeders in other places. As some kinds of 

 plants suffer much more from self-fertilisation than do 

 others, so it probably is with animals from too close 

 interbreeding. The effects of close interbreeding on 

 animals, judging again from plants, would be dete- 

 rioration in general vigour, including fertility, with no 

 necessary loss of excellence of form ; and this seems 

 to be the usual result. 



It is a common practice with horticulturists to 

 obtain seeds from another place having a very dif- 

 ferent soil, so as to avoid raising plants for a long 

 succession of generations under the same conditions ; 

 but with all the species which freely intercross by the 

 aid of insects or the wind, it would be an incomparably 

 better plan to obtain seeds of the required variety, 

 which had been raised for some generations under as 

 different conditions as possible, and sow them in 

 alternate rows with seeds matured in the old garden. 

 The two stocks would then intercross, with a thorough 

 blending of their whole organisations, and with no loss 

 of purity to the variety ; and this would yield far more 

 favourable results than a mere exchange of seeds. We 

 have seen in my experiments how wonderfully the 

 offspring profited in height, weight, hardiness, and fer- 

 tility, by crosses of this kind. For instance, plants of 

 Ipomoea thus crossed were to the intercrossed plants 

 of the same stock, with which they grew in competition, 



* Variation of Animals and Plants under Domesticat'on,' ch. xvii 

 2nd edit. vol. ii. pp. 98, 105. 



