Co-efficient of Variation. — It is often important to com- 

 pare the variability of different characters, by expressing 

 the Standard Deviation as a percentage of the average. In 

 the case of the beans the co-efficient of variation as to length 

 is 



1.1 



X 100 = 9.16. 



12 

 In the example of milk production cited above it is 

 1,770.1 



X 100= 32.1 



5515 



When the type of curve, the average and the standard 

 deviations and the co-efhcient of variation of a character are 

 known, the nature of the variation may be said to be fairly 

 well described. 



Bimodal Curves. — Sometimes curves show two modes 

 instead of one; such curves indicate either that the group is 

 breaking into two types or that two distinct types have 

 become mixed. 



Skew Curves — Sometimes curves are unsymmetrical, 

 and the mode lies considerably to one side of the average. 

 Such curves show the direction in which the variations are 

 tending. 



Exercises. — Find examples of organisms that show 

 (1) bimodal, (2) skew curves. 



Additional Exercises in Variations 



1. Plot the Curve and determine the Average and 

 Standard Deviations, and the Co-efficient of Variation in 

 the following analysis of sugar beets, after DeVries: — 



27 



