Periodical Literature 561 



In selecting, say, 4 average stems in each of 5 classes, making 

 20 sample trees, it is of less moment that the diameter be pre- 

 cisely correct, as that in form, height and branchiness they repre- 

 sent the average. 



Three trial choices made by three different persons showed 

 that the selection is quite practicable, the increment per cents 

 varying only between 2.64 and 2.77, while a carefully determined 

 per cent was 2.74. 



If ascertaining the increment per cent on standing sample 

 trees, the area increment (properly averaged) is found by the 



formula (Breymann's) ^ > to which the height increment 



per cent must be added, or else by the Borggreve averaging of 

 the Schneider formula which is somewhat more circumstantial 

 and less accurate. 



Some interesting relationships are brought out. According 

 to Schiffel, in spruce stands, if the trees are placed in five classes 

 of equal number arranged by diameters, then the diameters of 

 the average trees will be found to be possessed, beginning the 

 count with the lowest, at 10, 30, 51, 71, and 91 per cent of the 

 stem number. The author investigated this relation for pine, and 

 found the diameter of the average trees of five classes of equal 

 number at 10, 30, 50, 70, and 92 per cent of the stem number. 



If the classes are made with equal cross-section areas then 

 the average diameter lies — 



For spruce at 17, 48, 68, 84, 95 per cent 

 For pine at 18, 47, 68, 84, 96 per cent 



of the stem number. 



The class average diameters may also be calculated from the 

 average diameter of the whole stand, for, according to Schiffel, 

 the diameters of the average trees of the five classes of equal 

 number of stems lie at — 



I II III IV V 



69 84 96 109 136 per cent 



of the diameter of the average tree of the stand. (For instance, 

 if 20 inches were the diameter of the stand average tree, the 

 diameters of the class trees would be 13.8, 16.8, 19.2, 21.8, 27 

 inches.) 



