18 STATISTICAL METHODS. 



areas determined. But + = : thus a is deter- 



G a a 



mined. Knowing a we can get h^ or h 2 , and hence the mean. 

 Or the value of the character of the middle specimen may 

 be taken as the mean value. 



EXAMPLE. Seventy-six beech-leaves which had fallen from one 

 tree were picked up. They were sorted out as in the second method. 

 It was found that 22 were smaller than the smaller type leaf, which 

 was 1.78 inches in length; and 23 were larger than the larger type leaf 

 (2.22 inches in length). The 38th leaf is the middle of the series, and 

 so the smaller type leaf was distant 16 leaves from the middle, and 

 the larger 15. 



From Table IV: 



.21223 



.20884 



Therefore ^ = .555. 



Similarly = .5 



h 2 



A! = .2278, A 2 =-2122. 



Mean is at 1.78 + .2278 =2.01. 



