THEORY OF EVOLUTION 149 



FIG. 73. A curve resulting from arrangement of beans 

 according to size. (After de Vries.) 



The differences in size shown by the individ- 

 ual beans or by the individual men are due in 

 part to heredity, in part to the environment 



-3d *2d *d +d +26" +3<5 



FIG. 74. Curve of probability. (After Johannsen.) 



