graves: place of forestry among sciences 55 



of wood testing would be greatly simplified. Hardness was 

 also found to have a definite relation to the proportion of the 

 summer wood in the annual ring, and consequently to the specific 

 gravity of the wood. The specific gravity of wood is determined 

 by its anatomical structure, by the proportion of fibro-vascular 

 bundles, their thickness and length, the proportion of thick- 

 walled cells, medullary rays, etc. The anatomical structure in 

 its turn is probably determined by the combination of two 

 factors, — the amount of nourishment in the soil and the intensity 

 of transpiration. The mechanical properties of wood come, 

 therefore, within the control of the forester who raises and cares 

 for the forest. 



There is another field of scientific endeavor in which foresters 

 in this country may claim some credit. This is in the field of 

 forest mathematics. One unfamiliar with forest growth can 

 hardly realize the difficulties in the way of measuring the forest 

 crop, the amount of wood produced in a forest composed, for 

 instance, of many different species, sizes, and ages. If a tree 

 resembled any geometric body, such as a truncated cone, or an 

 Appolonian paraboloid, it would be a simple matter to determine 

 its contents by applying the formula for such body. But a 

 tree's form does not coincide with that of any known geometric 

 body, so that it would seem that the only possible way of determin- 

 ing the contents of the trees forming a forest would be by measur- 

 ing each single tree. Evidently this would be an entirely im- 

 practicable task. 



The common practice of determining the contents of trees 

 either in board measure or in cubic feet is to measure a large 

 number of trees of a given species in a given locality and apply 

 the average figures to the trees of the same diameters and heights 

 within that locality. Since there are, however, a great many 

 species of trees in this country, some of which have a very wide 

 geographic range, this method necessarily involves the prepa- 

 ration of a large number of local volume tables and hence the 

 measurement of hundreds of thousands of trees. The measure- 

 ment of tha taper of a larger number of trees has shown that 

 there are certain critical points along the stem of a tree, the 



