— 160 — 



Variability of diameters. 



In this table, S.D. and C. of V. represent the standard deviation and 

 coefficient of variation, respectively. Considering the given figures, we 

 arrive at these conclusions: — 



( i ) The more older, the more disperse as long as the stand remain 

 with the same grade of thinning ; the more heavier, the more less disperse 

 so long as the age is same. 



(ii) The more older, the distribution is the less variable when the 

 stand thinned with the same grade, and the heavier, the distribution is 

 the less variable when the age is the same. 



We think therefore that we are justified in treating the trees in a 

 stand a homogeneous when the age is greater or when the grade is 

 heavier. 



On comparing the mean diameter which was calculated by the first 

 moment and the corresponding probable errors we get the following 

 results. 



Age 

 in years 



32 

 37 

 41 

 47 

 52 



Comparison of Mean. 



stand with "a" grade 

 Mean 



7.568±0.226 

 9.577±0.238 

 I1.397±0.242 

 13-621 ±0.271 

 15.470±0.275 



Stand with " b " grade 

 Mean 



n.l96±0.216 

 12.061 ±0.211 

 12.589±0.225 

 14.660±0.256 

 16.517±0.265 



Stand with " c " grade 



Mean 



9.842±0.195 

 10.767±0.I81 

 13.441 ±0.232 

 16.119±0.266 

 18. 107 ±0.270 



Judging the given figures, we see that the greater the age, the greater 

 is the mean when the stand is thinned with the same grade; and that the 



