176 



GENERAL BOTANY 



and conclusions concerning experiments in cross-pollinating and 

 self-pollinating plants of the lupine (LupinuQ perennis). In this 

 case plants of the second generation were used for the experi- 

 ment. In his experiments with the garden pea (Pisum sativurti), 

 illustrated in the last table, Darwin secured results which 

 differed from those obtained in the majority of plants with 

 which he worked. This, as we shall see, is in harmony with 

 some recent results obtained by East, Shull, and other scientists. 



Morning-glory. The mean height of the self-fertilized plants in 

 each of the ten generations is also shown in the accompanying 



diagram, that of the inter- 

 crossed plants being taken at 

 100 ; and on the right side 

 we see the relative heights of 

 the seventy-three intercrossed 

 plants and of the seventy- 

 three self-fertilized plants. The' 

 difference in height between 

 the crossed and self-fertilized 

 plants will perhaps be best 

 appreciated by an illustration : 

 If all the men in a country 

 were on an average 6 feet high, 

 and there were some families 

 which had been long and 

 closely interbred, these would 

 be almost dwarfs, their average 

 height during ten generations 

 being only 4 feet 8^ inches. 



Diagram showing the mean heights of 

 the crossed and self-fertilized plants of 

 Ipomaeapurpurea in the ten generations, 

 the mean height of the crossed plants 

 being taken as 100. On the right hand 

 the mean heights of the crossed and self- 

 fertilized plants of all the generations 

 taken together are shown 



It should be especially ob- 

 served that the average differ- 

 ence between the crossed and 

 self-fertilized plants is not due 



to a few of the former having grown to an extraordinary height or 

 to a few of the self-fertilized having surpassed their self-fertilized 

 opponents, with the following few exceptions : the first occurred in 

 the sixth generation, in which the plant named Hero appeared ; two 

 in the eighth generation, but the self-fertilized plants in this genera- 

 tion were in an anomalous condition, as they grew at first at an 



