524 JOURNAL OF FORESTRY 



The spruce (Picea cxcelsa) was first studied. Jonson's first object 

 was to find a good system of classification. 



Trees of the same diameter and height may vary considerably in 

 volume content, owing to different taper. To express this variation in 

 form the form factors had been devised. The form factors, however, 

 are troublesome to arrive at, as they cannot be measured directly, it 

 being necessary first to compute the volumes of the tree carefully. 



The breast height form factor, hitherto in use, changes not only with 

 the form of the stem, but also with the height, and it is therefore not a 

 suitable expression of form, for the basal area of the cylinder is taken 

 at a proportionally greater height on a shorter tree. Therefore the 

 cylinder is smaller the shorter the tree is, and consequently, with an 

 increase of height, the form factor of trees of the same form is reduced. 



The Rinicker form factor, which is used to compare the portion of 

 the stem above breast height with a cylinder having a diameter equal to 

 the d. b. h. and a height equal to the height of the tree above breast 

 height, is a correct expression of form, but has not been used to any 

 gteat extent. 



The form quotient, first devised by Schiffel, is an excellent expres- 

 sion of stem form, however, and it is also very convenient, as it is 

 easily determined. 



The form quotient, according to Schiffel, is expressed algebraically : 



q = — -, d being the diameter at the middle of the stem, D the diameter 



at breast height, and q the form quotient. 



Professor Jonson does not, however, accept this formula unchanged, 

 for in this, as with breast height form factors, the classification is made 

 dependent on height, the two form-determining diameters not being in 

 the same relation to each other in trees of different height. For in- 

 stance: In classifying two conical trees, lo and 30 meters high above 

 stump, the diameter at the middle height of the tree will be compared 

 with d. b. h. at one-tenth of the height of the short tree and with 

 the d. b. h. at one-thirtieth of the height of the taller tree. This gives 

 the 10 m. tree form quotient 0.56 and the 30 m. tree form quotient 

 0.52. This, though both trees have the same (conical) stem form. 

 On a tree 2.6 meters high both measurements will be taken at 1.3 m.', 

 which gives q=i, or cylindrical form, while the tree may really have 

 any form at all without the form quotient being changed. Conse- 

 quently, trees of different heights must have different form to get into 

 the same "form class," which, of course, is illogical. This and other 

 inconsistencies disappear almost entirely, Jonson considers, if the 



