CHAP. XII. GENERAL RESULTS. 449 



derived from the same self-fertilised mother-plant 

 crossed by a fresh stock ; and the latter seedlings were 

 to the former in height as 100 to 52, and in fertility 

 as 100 to 4. An exactly parallel experiment was 

 tried on Dianthus, with this difference, that the plants 

 had been self-fertilised only for the three previous gene- 

 rations, and the result was similar though not so strongly 

 marked. The foregoing two cases of the offspring of 

 Ipomoea and Eschscholtzia, derived from a cross with a 

 fresh stock, being as much superior to the intercrossed 

 plants of the old stock, as these latter were to the self- 

 fertilised offspring, strongly support the same conclu- 

 sion. A cross with a fresh stock or with another variety 

 seems to be always highly beneficial, whether or 

 not the mother-plants have been intercrossed or self- 

 fertilised for several previous generations. The fact 

 that a cross between two flowers on the same plant 

 does no good or very little good, is likewise a strong 

 corroboration of our conclusion ; for the sexual 

 elements in the flowers on the same plant can rarely 

 have been differentiated, though this is possible, as 

 flower-buds are in one sense distinct individuals, 

 sometimes varying and differing from one another in 

 structure or constitution. Thus the proposition that 

 the benefit from cross-fertilisation depends on the 

 plants which are crossed having been subjected during 

 previous generations to somewhat different conditions, 

 or to their having varied from some unknown cause as 

 if they had been thus subjected, is securely fortified on 

 all sides. 



Before proceeding any further, the view which has 

 been maintained by several physiologists must be 

 noticed, namely, that all the evils from breeding 

 animals too closely, and no doubt, as they would say, 



2 a 



