16 



HEREDITY 



[CH. 



Another rather frequent condition is that the 

 curve has two maxima or modes (fig. 5), indicating 

 that a large number of individuals have a low measure- 

 ment, a less number are intermediate, and again a 

 larger number have a higher measurement Species 

 which vary in this way are called ' dimorphic/ or if 



300 



aoo 



100 



5 6 7 8 



Eig. 4. ' Half-cnrve ' representing the number of ' petals ' on 416 

 flowers of the marsh-marigold {Caltha palustrls). (After de Vries.) 



there are more than two peaks to the curve, 'poly- 

 morphic' Further, it is possible that the two parts 

 of the curve should be entirely separate, if inter- 

 mediates between the low and high groups are 

 completely wanting. This type of variation is spoken 

 of as ' discontinuous ' in contrast to the ' continuous ' 



