Chai\ II. SUMMARY OF OBSERVATIONS. 61 



descendants differed in constitution in an extraordinary 

 manner from ordinary plants of the present species. 



Although the plants raised during ten successive 

 generations from crosses between distinct yet inter- 

 related plants almost invariably exceeded in height, 

 constitutional vigour, and fertility their self-fertilised 

 opponents, it has been proved that seedlings raised 

 by intercrossing flowers on the same plant are by no 

 means superior, on the contrary are somewhat inferior 

 in height and weight, to seedlings raised from flowers 

 fertilised with their own pollen. This is a remarkable 

 fact, which seems to indicate that self-fertilisation is 

 in some manner more advantageous than crossing, 

 unless the cross brings with it, as is generally the case, 

 some decided and preponderant advantage ;<but to this 

 subject I shall recur in a future chapter. 



The benefits which so generally follow from a 

 cross between two plants apparently depend on the 

 two differing somewhat in constitution or character. 

 This is shown by the seedlings from the intercrossed 

 plants of the ninth generation, when crossed with 

 pollen from a fresh stock, being as superior in 

 height and almost as superior in fertility to the again 

 intercrossed plants, as these latter were to seedlings 

 from self-fertilised plants of the corresponding gene- 

 ration. We thus learn the important fact that the 

 mere act of crossing two distinct plants, which are 

 in some degree inter-related and which have been 

 lon^- subjected to nearly the same conditions, does 

 little good as compared with that from a cross between 

 plants belonging to different stocks or families, and 

 which have been subjected to somewhat different con- 

 ditions. We may attribute the good derived from 

 the crossing of the intercrossed plants during the 

 ten successive generations to their still differing some- 



