IM LUTHER BLHBANK 



In studying races of animals and plants, biol- 

 ogitts have diicorered that this t« km 



of aa tendency' to rerert to a meaii. i^ uin^ < i •>al. 



The matter has been especially studied in 

 recent years by the Danish biologist, Profensor 

 W. L. Johannaen, of Copenhagen. His studies 

 of barley and of kidney beans show that any 

 given race of these plants is really made up of a 

 number of subordinate races, representing diif( r- 

 ent strains of the ancestral pedigree, and that 

 when the plants are self-fertilized, the progeny 

 tend to group thetnaelves into a few more or len 

 permanent types. 



There are limits of variation as to size» color 

 and qualities, but the progeny as a whole do not 

 tend to have offspring that approach the halfwu 

 mark between these two extremes. Rather th< 

 break up into groups, each group tending t 

 reproduce itself in such a way as to form a new 

 subordinate race or "pure type." Thus from the 

 same mixed stock sundry races of relative giant 

 and of relative dwarfs, as well as nnmerons inter 

 mediate races, are formed. 



Now it would appear that such a case as that 

 of the prune, in which we are able to work out 

 by artificial selection a race characterized by 

 tendency to early fniitage, is in keeping with 

 these studies of the so-called "pure lines" of dt 



