Chap. VII. TABLE A. 281 



Lastly, with Pisum, Primula, the throe generations of 

 Canna, and the three of Nicotiana (which together 

 complete the twelve cases), a cross between two plants 

 certainly did no good or very little good to the off- 

 spring ; but we have reason to suspect that this is the 

 result of these plants having been self-fertilised and 

 cultivated under nearly uniform conditions for several 

 generations. The same result followed with the experi- 

 mental plants of Ipomcea and Mimulus, and to a certain 

 extent with some other species, which had been inten- 

 tionally treated by me in this manner; yet we know that 

 these species in their normal condition profit greatly by 

 being intercrossed. There is, therefore, not a single 

 case in Table A which affords decisive evidence against 

 the rule that a cross between plants, the progenitors of 

 which have been subjected to somewhat diversified 

 conditions, is beneficial to the offspring. This is a 

 surprising conclusion, for from the analogy of domesti- 

 cated animals it could not have been anticipated, that 

 the good effects of. crossing or the evil effects of self- 

 fertilisation would have been perceptible until the 

 plants had been thus treated for several generations. 



The results given in Table A may be looked at 

 under another point of view. Hitherto each genera- 

 tion has been considered as a separate case, of which 

 there are eighty-three ; and this no doubt is the more 

 correct method of comparing the crossed and self- 

 fertilised plants. 



But in those cases in which plants of the same 

 species were observed during several generations, a 

 general average of their heights in all the generations 

 together may be made ; and such averages are 

 given in Table A ; for instance, under Ipomcea the 

 general average for the plants of all ten generations 

 is as 100 for the crossed, to 77 for the self-fertilised 



