(29) 



7. In experiment 3, individual selection based on the 

 average spine number of the progeny of the individual 

 under consideration resulted in a rapid isolation of two 

 decidedly different strains within a single clone. 



8. Since the result in experiment 3 mighit have been due 

 to the appearance and preservation of a mutation, mass 

 selection was again tried. In experiment 4, on a very 

 favorable race ( as is shown by its high parental cor- 

 relation ), mass selection based on the external appear- 

 ance of the individual was sufficiently effective to 

 isolate two distinct strains from within a single clone. 

 In this experiment V^ll individuals were obtained, all 

 coming originally from a single specimen. 



9. In this experiment 4, something resembling a m.uta- 

 tion did appear. Its 39 progeny were traced out, and 



it was shcv/n that their elimination from the record makes 

 no essential change in the final result. 



Present status of the "pure line" hypothesis. In 

 considering the bearing of this work and other similar 

 investigations on the concept of the "pure line", one must 

 carefully distinguish between the two parts of which this 

 hypothesis is composed. The terK "pure line" was originally 

 applied to relatively constant diverse strains, discovered 

 within a single species. That such relatively constant 

 strains do occur in a great variety of plant and animal 

 species, is an observational fact, and has been reaffirmed 

 by every investigator who has entered this field. 



