534 JOURNAL OF FORESTRY 



It is not improbable that the formula for the stem curve of Norway 

 spruce will give correct results for our several spruce species and per- 

 haps other thin-barked conifers. Neither is it improbable that a true 

 expression for the stem form of other species may be obtained by in- 

 serting a new constant in the general formula, as was done by Jonson 

 for Scotch pine. This constant would probably vary for different 

 species ; it will be larger for a species the stem of which dissolves into 

 heavy branches than for a species with lighter branches. 



Jonson found that the form classes are, as a rule, fairly constant in 

 a stand and sometimes on whole forests. (Separate taper and volume 

 tables were made for each form class, 12 form classes being used. The 

 lowest is 0.525 and the highest 0.80, the interval between each class 

 being 0.025.) 



Objections may perhaps be raised by foresters to the task of securing 

 the diameter inside bark at breast height when analyzing sample trees. 

 This will probably not be necessary in regard to spruce, where all meas- 

 urements required to determine tree forms may be taken outside bark 

 if desired. 



In regard to thick-barked species, it will be necessary in accurate 

 work to make a cross-section at breast height on the test trees. An 

 increment borer may be used, but the portion of the bark in the core 

 will sometimes break and is then difificult to measure. - 



An intensive study of bark thickness should be carried on, so that the 

 relation between the stem forms with and without bark, and especially 

 at breast height, may be determined. 



All measurements should be taken with utmost care and only abso- 

 lutely normal trees should be selected as sample trees. 



" A new increment borer is now made by Beus & Mattson, Sweden. It has a 

 trough-shaped core extractor, permitting the core to be measured before it is 

 removed from the extractor. This instrument is used to great advantage in 

 measuring thickness of bark, according to Swedish foresters. 



