The Limits of Selection 



Pure: Line 



349 



Population 



Fig. 89. Johannsen's Pure Lines 



By intensive inbreeding of self-pollinating 

 beans, Johannsen established some nineteen pure 

 lines, all derived from a mixed population. A 

 large seed and a small seed from one such pure 

 line would yield identical progenies — that is, 

 groups having the same mode and the same range 

 of variation. Another pure line shows a differ- 

 ent mode and a different range, but overlapping 

 the range of variation of the first. It is possible, 

 therefore, to find a bean from each one of the 

 lines I, 2, 3, 4, and so on, that all appear to be 

 alike (phenotypes), and yet to obtain from each 

 of these similar seeds a distinct progeny (geno- 

 types). On being thrown together the seeds of 

 these several pure lines form a population pre- 

 senting a continuous series, as if they were all 

 members of the " same species." After Johannsen. 



