THE CLASSES OF FREQUENCY POLYGONS. 29 



terms of the standard deviation of the more variable of the 

 components.* 



The index of isolation of two masses of variates 

 grouped about adjacent modes is the ratio of the depression 

 between the modes to the height of the shorter mode. 



The meaning of multimodal curves is diverse. Sometimes 



\ 



FIG. 27. 



they indicate a polymorphic condition of the species, the modes 

 representing the different type forms. This is the case with 



3210123 



01234 



FIG. 28. 



the number of ray flowers of the white daisy which has modes 

 at 8, 13, 21, 34, etc. Sometimes they indicate a splitting of a 

 species into two or more varieties. 



* I have proposed (Science, VII, 685) to measure the divergence in a 

 unit = 3 X Standard Deviation, which has certain advantage in species 

 study. 



