Development of Forest Mensuration. 127 
being estimated at that time. He still made form 
classes for the same heights, but in 1823 simplified the 
method by assuming an average form factor for the 
whole stand. Even in 1830 Keenig still estimated the 
form factor, although he introduced the measurement of 
the cross-section area and determined the height indi- 
tectly as an average of measurement of several height 
classes, but Huber (1824) knew how to measure both 
the average height and form factor by means of an arith- 
metic sample tree. This method found entrance into 
the practice and held sway until about 1860 when the 
well-known improvements by Draudt and Urich sup- 
planted it. These last mentioned methods have become 
generally used in the practice while other methods like 
R. Hartig’s and Pressler’s have remained mainly theo- 
retical. 
The study of the increment and the making of yield 
tables which had been inaugurated by Oetellt, Paulsen, 
Hartig and others toward the end of the last century, 
was just at the end of that century placed upon a new 
basis through Spath (1797), who constructed the first 
growth curves by plotting the cubic contents of trees of 
different ages, and through Seutter (1799) by intro- 
ducing stem analysis, on which he based his yield tables. . 
On the shoulders of these did Hossfeld (1823) build, 
when he conceived the idea of using sample plots for con- 
tinued observation of the progress of increment and also 
taught the method of interpolation with limited meas- 
urements, laying the basis for quite elaborate formule. 
But the first normal yield tables, based on the average 
trees of an index stand, were published by Huber (1824) 
and in the same year by Hundeshagen. From that time 
