326 FERTILITY OP CROSSED CHAP. IX. 



fertilised flowers in the second table, G-, being 

 produced by self-fertilised parents, and the crossed 

 flowers by crossed parents, which in the later generations 

 had become somewhat closely inter-related, and had 

 been subjected all the time to nearly the same condi- 

 tions. These two tables include fifty cases relating to 

 thirty-two species. The flowers on many other species 

 were crossed and self-fertilised, but as only a few were 

 thus treated, the results cannot be trusted, as far as fer- 

 tility is concerned, and are not here given. Some other 

 cases have been rejected, as the plants were in an 

 unhealthy condition. If we look to the figures in the 

 two tables expressing the ratios between the mean 

 relative fertility of the crossed and self-fertilised 

 flowers, we see that in a majority of the cases (i.e., 

 in thirty-five out of fifty) flowers fertilised by pollen 

 from a distinct plant yield more, sometimes many more, 

 seeds than flowers fertilised with their own pollen ; and 

 they commonly set a larger proportion of capsules. The 

 degree of infertility of the self-fertilised flowers differs 

 extremely in the different species, and even, as we 

 shall see in the section on self-sterile plants, in the 

 individuals of the same species, as well as under 

 slightly changed conditions of life. Their fertility 

 ranges from zero to fertility equalling that of the 

 crossed flowers ; and of this fact no explanation can 

 be offered. There are fifteen cases in the two tables 

 in which the number of seeds per capsule produced by 

 the self-fertilised flowers equals or even exceeds that 

 yielded by the crossed flowers. Some few of these 

 cases are, I believe, accidental; that is, would not 

 recur on a second trial. This was apparently the 

 case with the plants of the fifth generation of Ipomoea, 

 and in one of the experiments with Dianthus. 

 Nicotiana offers the most anomalous case of any, 



