734 JOURNAI, OF FORESTRY 



growth. In this case a slow-growing 65 to 66-year-old stand, with 

 average d. b. h. of from 20 to 22 cm. and heights of 15 to 16.5 m., gave 

 the greatest yield, while the thriftiest stand, 89 to 100 years old, with 

 average d. b. h. of 32 cm. and height of 23 m., gave only a moderate 

 yield for the same dates. 



3. Mixed stands. There was no apparent difference due to mixtures 

 of other species, such as spruce and birch. 



4. Site conditions. (The area studied did not cover enough different 

 conditions to draw general conclusions.) 



(a) Soil. The yield was greater on sandy soil than on those 



which contained considerable clay, due, perhaps, to the 



warmer character of the sand. 

 (&) Exposure. No conclusions because of insufficient data, 

 (c) Slope. The yield was greater where the slope allowed the 



sun's rays to penetrate, 

 (rf) Altitude. The yield seems to decrease with altitude, due 



perhaps to decrease in soil temperatures. 



5. Meteorological conditions: 



(a) Atmospheric pressure. This is an important factor. The 



air pressure opposes the internal pressures which force 

 the resin out, so the lower the barometer the greater the 

 flow of resin. 



(b) Air temperature. The flow tends to increase with increase 



in temperature, except that on hot, dry days the resin may 

 harden and stop the flow. 



(c) Humidity. The flow is greatest on sultry days. 



6. Frequency of zvorking. The ducts become stopped up with har- 

 dened resin within 24 hours, and 24 hours more is required to restore 

 the original pressure. Cutting should therefore be repeated every two 

 days, and the resin harvested at the end of the first day after cutting, so 

 as not to lose part of it by evaporation. 



7. Distribution of zvork. Where possible, stands should be worked 

 in units of such size that loss of time due to travel is avoided. There 

 should be enough laborers to work the stands regularly at two-day 

 intervals. One person can cut about eight hundred faces per day. 



Forstmeister Koehl, of Trippstadt, contributes the following to the 

 discussion of methods of turpentining. His experiments were made 

 on a 25-hectare tract of 99 to 103 year-old Scotch pine, partly mixed 



