54 IPOMCEA PUEPUEEA. CHAP. II 



It should be especially observed that the average dif- 

 ference between the crossed and self-fertilised plants 

 is not due to a few of the former having grown to an 

 extraordinary height, or to a few of the self-fertilised 

 being extremely short, but to all the crossed plants 

 having surpassed their self-fertilised opponents, with 

 the few following exceptions. The first occurred in 

 the sixth generation, in which the plant named " Hero'" 

 appeared ; two in the eighth generation, but the self- 

 fertilised plants in this generation were in an anomalous 

 condition, as they grew at first at an unusual rate and 

 conquered for a time the opposed crossed plants ; and 

 two exceptions in the ninth generation, though one 

 of these plants only equalled its crossed opponent. 

 Therefore, of the seventy-three crossed plants, sixty- 

 eight grew to a greater height than the self-fertilised 

 plants, to which they were opposed. 



In the right-hand column of figures, the difference 

 in height between the crossed and self-fertilised plants 

 in the successive generations is seen to fluctuate much, 

 as might indeed have been expected from the small 

 number of plants measured in each generation being 

 insufficient to give a fair average. It should be 

 remembered that the absolute height of the plants 

 goes for nothing, as each pair was measured as 

 soon as one of them had twined up to the summit 

 of its rod. The great difference in the tenth genera- 

 tion, viz., 100 to 54, no doubt was partly accidental, 

 though, when these plants were weighed, the differ- 

 ence was even greater, viz., 100 to 44. The smallest 

 amount of difference occurred in the fourth and the 

 eighth generations, and this was apparently due to 

 both the crossed and self-fertilised plants having 

 become unhealthy, which prevented the former attain- 

 ing their usual degree of superiority. This was an 



