730 JOURNAL OF FORESTRY 



taken care of by the use of pitch distilled from resinous wood, while 

 the sticky-fly paper industry used coumaron. 



Domestic production concerns chiefly the pine forests, although a 

 certain amount can be obtained from the spruce. 



Under the stimulus of the Resin Section of the committee the tur- 

 pentining of pine forests was undertaken in many parts of Germany, 

 and many foresters undertook to study the best methods for carrying 

 on the business. 



Tubeuf undertakes to explain the origin of the flow of resin, as a 

 basis for organizing production. According to him, the resin, secreted 

 in some manner from the food materials stored in the living paren- 

 chyma tissue which lines the walls of the resin ducts, is under pressure 

 due to the turgidity (Turgordriick) of the lining cells. When one of 

 these ducts is cut across, the pressure forces the resin, or "balsam," 

 out, until internal and external pressure are equalized. Meanwhile the 

 opening in the duct becomes sealed up again as the volatile part of the 

 resin evaporates, so that internal pressure is restored and another flow 

 results if the canal is again opened up after a short interval. The resin 

 ducts, which run both vertically with the wood fibers and horizontally 

 with the medullary rays, are all more or less joined up in one system, 

 but the individual ducts are rather short (15 to 70 cm.), so that new 

 cuts are likely to open new ducts and thereby increase the flow of resin. 

 The production of resin depends on the number of resin ducts in the 

 wood. Since these are mostly in the late summer or fall wood, their 

 number is to a considerable degree dependent on the breadth of the 

 rings and the proportion of late wood in them. Living tissue is present 

 only in the sapwood of the pine. 



Not only does the secretion of resin by different trees vary very 

 widely, but the yields, even of trees which contain equal amounts of 

 resin, also differ, due to differences in cell turgidity. This turgidity 

 depends on the water content of the tree, which in turn depends on its 

 vegetative condition, on its intake and output of water. These are in- 

 fluenced to a great extent by outside factors, such as temperature of 

 soil and air, soil moisture, humidity. Conifers which absorb no water 

 in winter, but continue to evaporate it through their foliage, are poorest 

 in water and lowest in turgidity in April and the first part of May. 

 The greatest pressure is exerted when, due to soil warmth and moisture, 

 more water is taken in than the leaves evaporate. This occurs in July 

 and August and as late as October. Warm rains and warm sultry 

 periods are especially favorable to abundant flow of resin, while cold 

 spells or hot drying winds are unfavorable. For the same reason. 



