738 JOURNAL OF fore;stry 



cut and sometimes double the distance (Tschirch). Scraping can often 

 considerably increase the yield of poor yielders. Biehler's conclusion 

 is that the method of working has the greatest effect on resin yield, 

 while uncontrollable factors such as soil and weather are of secondary 

 importance. Much further study is needed to develop the proper 

 technique. 



The Resin Section of the War Committee for Vegetable and Animal 

 Oils and Fats (Kreigsausschuss fiir pflanzliche und tierische Ole und 

 Fette, Rohharzabteilung) published a somewhat detailed memorandum 

 of suggestions and instructions for the production of resin during the 

 season 1918. The American groove (Risser) method is recommended, 

 with cuts embracing two-thirds of the circumference of the stem (or 

 twice the diameter), except that trees to be cut the next year can be 

 worked more intensively. Faces should be prepared by removing the 

 outer bark from the ground to one meter high. Trees to be worked on 

 only one side should be cut on the northeast to protect against sun, 

 wind, and rain, and also because the rate of growth, and consequently 

 the yield, is apt to be greatest on that side. In grooving, a plumb-bob 

 should be used to get the center groove vertical. The grooving knife 

 should be sharpened with a whetstone every hour. Either of two 

 forms of grooving may be used: (a) The herring-bone (Splettstosser) 

 system, leaving a narrow space between successive grooves; (b) the 

 American system, which cuts along the edge of the previous cut. (The 

 cutting from below upward, as is done in America, is more wasteful of 

 resin than cutting from above downward.) 



The committee states that it is uncertain which of the two methods 

 is the better, but it is believed that the herring-bone method gets more 

 resin with the least work, while the American method allows longer 

 working of the same tree and therefore more resin in the long run. 

 The extensive use of the first is recommended in order to get quick 

 results on account of war needs. 



The best yield is from downward working during the first 4 to 8 and 

 in some cases 8 to 12 weeks; therefore the first cut should be made 

 about 60 cm. from the ground, and following cuts during the next 4 

 weeks or so should be made below it. Later (the time to be deter- 

 mined by trial) cuts may be made upward. If convenient, a 30-cm. 

 strip should be left at the bottom to start the second year with. 



While grooves i cm. deep in the wood yield slightly more at first, 

 shallow cuts, which are easier to make, yield as much in the long run. 

 Cuts from 2 to 5 mm. deep are recommended. A two to three days' 

 interval between cvits is recommended for Avarm weather, and four to 

 five days in cool, damp weather. 



