618 
Journal of Agricultural Research 
Vol. XXX, No 7 
irregularly from height class to height 
class. In all the work done by the 
author little adjustment of this kind has 
been necessary. 
From these final curves the true 
absolute form quotient for each size 
class may be read. The next step is 
to select a number of the original taper 
curves which have a good basis in 
number of trees and yet show a wide 
variation in form quotients. After 
selecting 20 or 30 of these, the distance 
between breast height and the tip of 
the tree should be divided into 10 
equal parts (fig. 6). The diameter of 
each one of these points up the tree is 
then read off and put down on paper. 
After this is done, each of these diame- 
example of Douglas fir, here used, they 
fall into very good lines and require 
little study in order to draw the proper 
curves. The curve at 0.5 of the way 
up the tree must be a straight line 
because that is the form quotient line. 
The. lines representing the diameter 
percentage at 40, 30, 20, and 10 per 
cent of the height of the tree also 
apparently fall in straight lines, which 
when extended meet at ordinate value 
1.0 and abscissa value 1.0. At 60, 
70, 80, and 90 per cent of the tree 
height they are flat smooth curves. 
After drawing these curves it is pos¬ 
sible to read off the proper subordinate 
form quotients for any diameter and 
height class after reading the proper 
Fig. 6 —Diameter inside bark curve subdivided to determine subordinate form quotients for 16 inch- 
100 foot class Douglas fir 
ters is divided by the d. b. h. inside 
bark of the tree from which they were 
taken, this being done very rapidly and 
with ample accuracy by slide rule. In 
this way a series of subordinate form 
quotients are obtained, showing the 
diameter at 10 points equidistant up 
the tree in percentage of diameter 
breast high. 
In order to even off these values a 
series of curves should be made, with 
the form quotient as the abscissa and 
the subordinate percentages or form 
quotients the ordinate. All the values 
which have been computed should be 
plotted on a single graph according 
to the appropriate form quotient of 
the tree, as shown in Figure 7. In the 
form quotient from the curves already 
prepared (as in fig. 5 for the 100-foot 
class). It is a simple thing then to 
prepare a taper table if the proper 
base diameter is known for each d. b. h. 
class of trees. This can easily be ascer¬ 
tained by plotting the d. b. h. inside 
the bark from the curves first drawn 
against the d. b. h. outside the bark for 
each diameter class (fig. 8). Variations 
can easily be smoothed out by simple 
curving. 
Now, having the correct diameter 
inside the bark, the correct form quo¬ 
tient, and the correct subordinate form 
quotients all the way up the tree, it is 
a simple matter to draw smooth and 
correct taper curves by applying the 
