56 IPOMGEA PURPUKEA. CHAP. IL 



mother-plant, that many of the crossed plants in each 

 generation were related, often closely related, and that 

 all were exposed to the same conditions, which, as we 

 shall hereafter find, is a very important circumstance, it 

 is not at all surprising that the difference between 

 them should have somewhat decreased in the later 

 generations. It is, on the contrary, an astonishing fact, 

 that the crossed plants should have been victorious, 

 even to a slight degree, over the self-fertilised plants 

 of the later generations. 



The much greater constitutional vigour of the 

 crossed than of the self-fertilised plants, was proved on 

 five occasions in various ways ; namely, by exposing 

 them, while young, to a low temperature or to a 

 sudden change of temperature, or by growing them, 

 under very unfavourable conditions, in competition 

 with full-grown plants of other kinds. 



With respect to the productiveness of the crossed 

 and self-fertilised plants of the successive generations, 

 my observations unfortunately were not made on any 

 uniform plan, partly from the want of time, and partly 

 from not having at first intended to observe more than 

 a single generation. A summary of the results is here 

 given in a tabulated form, the fertility of the crossed 

 plants being taken as 100. 



First Generation of crossed and self-fertilised Plants 

 growing in competition with one another. Sixty-five 

 capsules produced from flowers on five crossed plants 

 fertilised by pollen from a distinct plant, and fifty-five 

 capsules produced from flowers on five self-fertilised 

 plants fertilised by their own pollen, contained seeds 

 in the proportion of 100 to 93 



Fifty-six spontaneously self-fertilised capsules on 

 the above five crossed plants, and twenty-five sponta- 

 neously self-fertilised capsules on the above five self- 

 fertilised plants, yielded seeds in the proportion of . 100 to 99 



