726 JOURNAL OF FORESTRY 



tained by measurement and the mean diameter which by empirical 

 knowledge was to be expected, must also be taken into consideration. 



The thickness of bark at breast height and the taper of the bark with 

 increasing height on stem is thoroughly investigated. Series of rela- 

 tive bark percentages breast high were obtained from all sample plots 

 and an average relative series was worked out. By means of this 

 series the bark percentage for each diameter class in a stand can be 

 found as soon as the value for one class is known. It is found that the 

 bark percentages breast high decrease with increasing d. b. h. The 

 general thickness of the bark in different stands varies a good deal, this 

 being considered due, probably, to the difference in the origin of the 

 seed. Taper series for the bark of trees of different height classes 

 were reduced in the same manner as was before used in dealing with 

 the taper of the stem. Since the taper of the bark is a quality quite 

 independent of the taper of the stem, the absolute form quotient was 

 put aside and the bark quotient at the middle of the stem was used as 

 a measure of taper. 



Having obtained taper series for stem and bark, Mattsson works out 

 for each form-height group breast height form factor for the stem in- 

 side bark and for the bark relating to the cylinder inside the bark. A 

 table showing the volume of bark in percentage of the volume of stem 

 inside bark for stems of different form quotients and bark quotients at 

 the middle of the stem is also worked out. 



H. C.-W. 



Meddelanden fran Statens Skogsforsoksanstalt, 1917, pp. 843-922. 



UTILIZATION, MARKET, AND TECHNOLOGY 



W. B. Campbell, of the Canadian Forest Prod- 



Puel ucts Laboratory, explains in simple language how 



Value the fuel value of woods is determined. As the 



of subject is nowadays of increased interest, we 



Wood quote in full : 



For every combustible substance there is a cor- 

 responding "heat of combustion," which is invariable for that substance 

 and is expressed as the number of heat units, or B. T. U.'s (British 

 thermal units), given off by the combustion of one pound. This quan- 

 tity is the same, no matter how slowly or how rapidly the combustion 

 takes place, and it has no direct reference to the temperature of the fire. 

 If combustion is rapid, a large number of heat units are produced in a 



