Periodical Literature. 287 



Precise investigations, by which to learn to estimate site classes, 

 are required. Such are conducted by Leininger in the soil labora- 

 tory of Tharandt. He gives examples of his investigations. 



The first investigation concerned itself with the question 

 whether the average height can be used as index of site classes. 

 This index had already been pointed out by Oettelt in 1765. 

 Again Baur in 1870 called attention to this relation, pointing 

 out that in stands of approximately the same age the volumes were 

 proportionate to the average heights. And ever since this factor 

 has been utilized for site classification in yield tables. 



The justification for relying on this factor is established by 

 careful ascertainment of the heights after the Draudt-Urich 

 method, and relating them to Kunz's yield tables. 



The relation of the average height to certain soil qualities on 

 the same rock formation is then investigated, namely the hygro- 

 scopicity at 15.6° C and 91% relative humidity of the soil and the 

 ability for nitrogen, known as Knop's absorption coefficient. All 

 investigations so far have shown that on same rock and at same 

 elevation great parallelism between average height of stands, 

 hygroscopicity of the fine earth and Knop's coefficient exists. 



The author points out that one of the most difficult tasks of the 

 soil investigations is the taking of samples and complains that so 

 often no data are furnished by investigators how the sampling 

 was done. The necessity of a large number of samples evenly 

 distributed and taken to the same depth is accentuated and the 

 method used described in detail. The necessity of investigating 

 the soil in layers is explained; a table showing the variation of 

 lime contents and exhibiting the great changes with depths. The 

 different layers must be measured. For the shallow-rooted spruce 

 a depth of 12 inches seems sufficient ; for pine, a greater depth 

 would appear necessary to investigate. 



In determining the volume of pores, which is of great impor- 

 tance, if, as is done at Tharandt, the nutritive elements are related 

 to the space and not to weight of the soil, great variety of pro- 

 cedure seems to exist. 



Since the pore volume cannot be determined from the usual 

 sample after it is taken, special samples for the purpose are 

 secured by Schermbeek's sampler, specially fitted for the purpose. 

 The contents are measured, not weighed to .1 mm. 



