444 GENERAL RESULTS. CHAP. XII. 



any corresponding degree on the pollen of the self- 

 fertilised parents acting inefficiently on the stigmas of 

 the same flowers; for in the case of the Ipomosa, 

 Mimulus, Digitalis, Brassica, &c., the self-fertilised 

 parents yielded an abundant supply of seeds ; never- 

 theless the plants raised from these seeds were 

 markedly inferior in many ways to their cross-ferti- 

 lised brethren. Again with Eeseda and Eschscholtzia 

 the more self-sterile individuals profited in a less 

 degree by cross-fertilisation than did the more self- 

 fertile individuals. With animals no manifest evil 

 has been observed to follow in the first few generations 

 from close interbreeding ; but then we must remember 

 that the closest possible interbreeding with animals, 

 that is, between brothers and sisters, cannot be con- 

 sidered as nearly so close a union as that between the 

 pollen and ovules of the same flower. Whether with 

 plants the evil from self-fertilisation goes on increas- 

 ing during successive generations is not as yet known ; 

 but we may infer from my experiments that the increase, 

 if any, is far from rapid. After plants have been pro- 

 pagated by self-fertilisation for several generations, a 

 single cross with a fresh stock restores their pristine 

 vigour ; and we have a strictly analogous result with 

 our domestic animals.* The good effects of cross-fer- 

 tilisation are transmitted by plants to the next gene- 

 ration ; and judging from the varieties of the comma : 

 pea, to many succeeding generations. But this may 

 merely be that crossed plants of the first generation 

 are extremely vigorous, and transmit their vigour, like 

 any other character, to their successors. 



The means for favouring cross-fertilisation and pre- 

 venting self-fertilisation, or conversely for favouring 



* * Variation under Domestication,' ch. xix. 2nd edit. vol. ii. p. 159. 



