RKGIONAL VOLUME TABLE 725 



Pathology, and l)y him most kindly made available for this work. The 

 diameter measurements on these trees were taken, however, at vary- 

 ing heights dependent on the location of rot within the boles, and did 

 not always extend far enough into the tops to be useable. About half 

 of these data had to be discarded on this account. 



The Forest Service data, moreover, having been collected at many 

 different places and by different observers, were none too w^ell stand- 

 ardized in form. 



THE TAPER CURVES 



Obviously the only way in which such data could be combined, 

 was by drawing taper curves for each height-diameter class. This 

 was therefore done, the class intervals adopted being 2 inches for 

 d. b. h., 16 feet for total height, and a separate set of curves being 

 prepared for each major locality. The resulting curves numbered 

 over 400, not including a considerable number which had to be 

 thrown out due to inadequate data. 



FORM QUOTIENTS 



It was obviously desirable to combine as many as possible of the 

 groups and so have the minimum number of volume tables. As a 

 criterion of the advisability of attempting this, the form quotient for 

 each taper curve was calculated. For simplicity, this was defined as 

 the ratio between d. i. b. at the mid-point and d. b. h. Tables were pre- 

 pared for each group giving form quotients by height and diameter 

 classes. A characteristic result follows in Table 2. 



It seems fairly evident in this case (and all other cases were similar) 

 that form quotients do not vary with either height or diameter to 

 a perceptible degree, within a given group. An average form quo- 

 tient may, therefore, be used for each such group. When these were 

 calculated, it was found that they ranged from a minimum of .53 to 

 a maximum of .61. A few rough tests made it obvious that form fac- 

 tors varied more, rather than less than form quotients, so the above 

 figures meant differences of form between localities of at least 15 

 per cent.^ This is obviously too great to justify combination into a 

 single volume table. 



*As will be shown later the form differences were finally found to exceed 20 

 per cent. 



