YIELD TABLES 77 



the basal area of the average stem for each pe- 

 riod, and the result is the number of trees per 

 acre. 



It will be seen that the number of trees per 

 acre increases as the locality grows poorer. 

 This is easily explained by the smaller size of 

 the individual trees. 



Form factors were computed for the volume 

 with bark to serve as a control for the tables. 

 It wiU be seen that the form factors at first fall 

 off and after a certain point rise again, and 

 that they are larger the poorer the quality of 

 the locality. 



