No. 534] 



THE PURE LINE THEORY 



357 



and low oil and protein selection in maize, their work has 

 been merely the isolation of pure and constant strains — 

 " sub-races" — with the characteristics in question as 

 strongly developed in the beginning as we now find them, 

 but continually intercrossing. The case is too compli- 

 cated for discussion in detail, but certainly the fact that 

 the characters can no longer be increased by selection 24 

 is no strong argument for the biotype idea. Under its 

 present morphological and physiological organization we 

 have no reason to suppose that the corn grain can be 

 made to contain as much oil as the castor bean. 



Again Pearl and Surface 25 announce concerning their 

 selection work with corn, 



We find the results of this experiment or investigation to be very 

 difficult (if not altogether incapable) of rational explanation in accord- 

 ance with the biological implications of the " law of ancestral inherit- 

 ance " and conclude that the results agree better with the genotype 

 theory of Johannsen than with that of the cumulative theory of selection 

 with, of course, the limitations implied by the fact that it is an open 

 fertilized plant. 



What Pearl and Surface have actually done is to take 

 a desirable sweet corn which they for convenience desig- 

 nate as Type I, and attempt — with initial success — to 

 improve it for yield in ears and stover, for configuration 

 of ears, and especially for earl mess. But this Type I 

 corn is descended from a few ears, the offspring of which 

 have been grown in Maine for fifteen to twenty-five years. 

 The variety originally introduced must have been an 



21 That changes due to selection are at first rapid and then slower has 

 long been recognised. Indeed, as early as 18(59 Ilallett stated as two of his 

 laws of the action of selection, "The improvement which is at first rapid, 



Me. Ag. Exp. Sta. Bull., 1910. 



