VARIATION 



31 



not always give a bimodal curve. For example, if Pear- 

 son's two lots of beech leaves mentioned above are 

 mixed together, they form a regular series from the 

 inspection of which no one could infer their double 

 origin. (See the heavy line in Figure 7.) 



12 



Number 

 ofriba 



14 15 16 17 18 19 20 21 



FIG. 7. The ribs of leaves from two beech trees. When put 

 together they form a polygon which does not reveal its double 

 origin. From data by Pearson. 



c. Skew Curves 



The direction in which variations are tending may 

 sometimes be determined by the statistical method. As 

 an illustration of this may be cited the number of ray 

 florets in 1000 white daisies (Chrysanthemum leucanthe- 

 mum), 500 of which were collected at random by the 

 writer from a small patch in a swampy meadow in 

 northern Vermont, while the other 500 were selected 

 in the same random manner upon the same day from a 

 dry hillside pasture hardly more than a stone's throw 



