THE PURE LINE 107 



fectual so far as inheritance is concerned, and it 

 makes no difference whether the largest or the small- 

 est beans within a pure line are selected from which 

 to breed, the result will be the same, in that there is a 

 complete return to mediocrity or type with no "in- 

 heritance" of the parental modification. As a 

 matter of fact in 1903, 1906 and 1907 the lighter 

 parents gave a heavier progeny than the heavier 

 parents. 



It will be seen at once that here is a discovery of 

 far-reaching importance which may require us to 

 reconstruct certain cherished ideas about the part 

 played in the evolution of species, as well as in 

 heredity, by natural selection. 



5. Cases similar to Johanssen's Pure Lines 



Although according to Johanssen pure lines are 

 *'the progeny of a single self -fertilized individual," 

 it is plain that in at least three other possible cases 

 something quite similar to "pure lines" may be 

 obtained. 



First, when two similar organisms identical in 

 their germinal determiners with regard to a particular 

 character inbreed, their progeny will form a pure line 

 so far as this particular character is concerned just as 

 truly as two parents that are united in a single in- 

 dividual produce a pure line progeny as the result of 

 self-fertilization. 



Second, in cases of parthenogenesis, the progeny 

 arising from a single female individual without the 

 customary qualitative reduction of chromosomes that 



