THE STATISTICAL STUDY OF EVOLUTION. 453 



interpretation is still to Ije worked out. The beginnings are, however, 

 instructive. 



A-^ariation polygons are of two main sorts — simple and complex. 

 Simple variation polygons possess only a single mode, whilst complex 



Fig. 6. Types OF FBEiji'ENCY Cuhves. From K. Peakson. 



polygons usually show a trace of more than one mode. Simple varia- 

 tion polygons are of several types. Some are symmetrical about the 

 mode as in Fig. 5. Others are more or less iins}anmetrical or skew, as 



t li t\ IS M 4t m a 20 II U U ^« 25 2« 27 £6 



Fig. 7. Cvkves of vssEi.ErTED and selected lots of white daisies. 



curves of frequencies of various members of ray flowers IX WILD DAISIES. 



" " " ■' •■ ■' •• IX descexdaxts of 12 or 



18-RAYEDWILD DAISIES. 



. " " " " " OF RAY FLOWERS IX DESCEXDAXTS of 21-RAY-ED 



WILD DAISIES. 



they are technically called (Fig. 6). Skew polygons usually tail out 

 at the base further from the mode on one side than on the other. The 

 polygon is said to be skew in the direction of this longer partial base. 

 Why some distributions are symmetrical and others skew is not fully 



