Periodical Literature 159 



sirably cannot be maintained. He even concludes, that "every 

 increase in the degree of thinning up to the C grade improves the 

 shaft form (reduces the taper), and especially the part above the 

 middle of the shaft improves in form." 



To this statement, which is in contradiction of all experience, 

 SchiflFel takes exception, and finds the error of the deduction in 

 the mathematical method employed for utilizing the data, namely 

 by comparing the quotients of diameters at different heights di- 

 vided by the diameter in the middle of the shaft, not of all the 

 trees but of trees of the same height and diameter. All that is 

 thereby proved is Schiffel's prior finding, namely that on similar 

 sites trees of the same height and diameter have the same form 

 factor. 



Basing the diameter quotient on the diameter in the middle of 

 the shaft is also objectionable since that implies at once grouping 

 by equal heights 



Schiffel then makes the comparison of the average trees, using 

 a diameter quotient based on diameters of symmetrical parts, 

 namely d^|^ : d^n = q^,^. These quotients for the same diameter 

 class remain nearly constant under all degrees of thinning, as 

 shown by Kuutze, and hence permit the forming of averages 

 of stems taken from any thinning area, thinned to any degree, 

 for the purpose of determining whether one or the other degree 

 of thinning produces more or less taper. 



The comparison of these diameter quotients in different dia- 

 meter classes show that they sink with increasing diameter, just 

 as is known to be the case with form factors, and a comparison 

 of the diameter quotients of the average trees shows that they 

 sink, although not much with increase in the degree of thin- 

 ning, /. e., the proposition that every increase in the degree of 

 thinning produces more cylindrical form is not proved. The op- 

 posite is more likely true. 



The investigations, however, prove that on medium to poor 

 sites a severer thinning which does not interrupt the crown cover 

 for some time produces no noticeable difference in volume or 

 form accretion, if the thinning is made in the later polewood 

 stage after the clearing process is well completed. If, on the 

 other hand, open plantations or stands opened in early life were 

 compared with continuously dense growths, the relation of shaft 

 form and crown density would at once be apparent, namely one 

 extreme form represented in the open and the other extreme in 



