28 IPOMCEA PURPUREA. CiUP. II 



CIIAPTER II. 



CONVOLVULACEJJ. 



Iponicea purpurea, comparison of the height and fertility of th* 

 crossed and self-fertilised plants during ten successive generations 

 Greater constitutional vigour of the crossed plants The effects 

 on the offspring of crossing different flowers on the same plant, 

 instead of crossing distinct individuals The effects of a cross with 

 a fresh stock The descendants of the self-fertilised plant named 

 Hero Summary on the growth, vigour, and fertility of the suc- 

 cessive crossed and self-fertilised generations Small amount of 

 pollen in the anthers of the self-fertilised plants of the later genera- 

 tions, and the sterility of their first-produced flowers Uniform 

 colour of the flowers produced hy the self-fertilised plants The 

 advantage from a cross between two distinct plants depends on their 

 differing in constitution. 



A plant of Ipomoea purpurea, or as it is often called in 

 England the convolvulus major, a native of South 

 America, grew in my greenhouse. Ten flowers on this 

 plant were fertilised with pollen from the same flower ; 

 and ten other flowers on the same plant were crossed 

 with pollen from a distinct plant. The fertilisation of 

 the flowers with their own pollen was superfluous, as 

 this convolvulus is highly self-fertile ; but I acted in 

 this manner to make the experiments correspond in all 

 respects. Whilst the flowers are young the stigma 

 projects beyond the anthers ; and it might have been 

 thought that it could not be fertilised without the aid 

 of humble-bees, which often visit the flowers ; but as 

 the flower grows older the stamens increase in length, 

 and their anthers brush against the stigma, which thus 



