to the mean of its particular line, but not to the mean of the 

 variety. 



Johannsen first used the term "Pure Line'' in a pam- 

 phlet entitled On Inheritance in Populations and in Pure 

 Lines, published in 1903, giving the results of a long series 

 of experiments carried out with beans and barley. A Pure 

 Line includes all the descendants of a single individual be- 

 longing to a strain which is reproduced exclusively by 

 self-fertilization. It may be noted that in a Pure Line the 

 germ plasm is never mixed, as it is derived from the same 

 parent and there is no chance for new combinations of 

 characters derived from different parents. 



Let us examine for a moment the results obtained by 

 Johannsen. In the case of the beans, 19 Pure Lines were 

 grown from 19 different original plants. When all the beans 



Fig. 12. — Pure lines of beans. Tlie lower figure gives the general 

 population, the other figures give the pure lines within the popula- 

 tion (After Johannsen.). 



were thrown together and arranged as to size a normal curve 

 of frequency was obtained, which showed that the popula- 

 tion belonged to a single type. The average weight was 

 478.9 milligrams, and the standard deviation 95.3 mgms. 

 (Fig. 12). 



When, however, the 19 separate Pure Lines were 

 examined as to size, each had its own normal curve of fre- 

 quency and its own standard deviation. Average weight 

 ranged from 351 to 642 mgms. and the standard deviation 

 from 64 to 109 mgms according to the following table: 



