CHAP. VII. TABLE O. 269 



by the other figures how wonderfully superior they 

 are both to the self-fertilised and to the intercrossed 

 plants of the same stock. With respect to height and 

 weight, there are only two exceptions to the rule, 

 namely, with Eschscholtzia and Petunia, and the 

 latter is probably no real exception. Nor do these 

 two species offer an exception in regard to fertility, 

 for the plants derived from the cross with a fresh stock 

 .vere much more fertile than the self-fertilised plants. 

 The difference between the two sets of plants in the 

 table is generally much greater in fertility than in 

 height or weight. On the other hand, with some of 

 the species, as with Nicotiana, there was no difference 

 in fertility between the two sets, although a great dif- 

 ference in height and weight. Considering all the 

 cases in this table, there can be no doubt that plants 

 profit immensely, though in different ways, by a cross 

 with a fresh stock or with a distinct sub-variety. It 

 cannot be maintained that the benefit thus derived is 

 due merely to the plants of the fresh stock being per- 

 fectly healthy, whilst those which had been long inter- 

 crossed or self-fertilised had become unhealthy ; for in 

 most cases there was no appearance of such unhealthi- 

 ness, and we shall see under Table A that the inter- 

 crossed plants of the same stock are generally superior 

 to a certain extent to the self-fertilised, both lots 

 having been subjected to exactly the same conditions 

 and being equally healthy or unhealthy. 



We further learn from Table C, that a cross between 

 plants that have been self-fertilised during several 

 successive generations and kept all the time under 

 nearly uniform conditions, does not benefit the offspring 

 in the least or only in a very slight degree. Mimulus 

 and the descendants of Ipomrea named Hero offer 

 instances of this rule. Again, plants self-fertilised 



