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MISC. PUBLICATION 257, U. S. DEPT. OF AGRICULTURE 



weighing again, the difference indicating the percentage of green 

 weight. 



R. Hartig (87) found that the water content varied between 30 and 

 60 percent in the 30 different species which he examined and in the 

 same species at different seasons of the year; but if the curves showing 

 the variation in water content of the various species throughout the 

 year are compared, they show on the whole a marked parallelism. 

 The highest water content occurs from December to March during 

 the dormant period of the year and the lowest in June to September 

 when the trees are most active. If a hardwood, such as the beech, is 

 compared with a conifer, like the pine, it will be seen, however, that 

 the water content of the beech sinks very much between July and 

 October, while that of the pine sinks very little during this period. 

 After the transpiration is diminished by the fall of the leaves, in the 

 case of the beech, and by the onset of cooler weather, in the case of 

 the pine, both trees show an increase in their water content which 

 continues until the following spring. The same differences are seen 

 if one compares spruce and oak. 



Studies on this subject were also made by T. Hartig (90), who 

 measured the water content of stems, roots, and leaves for 3- to 

 5-year-old trees of pine, spruce, oak, and beech. In the conifers the 

 root and stem have a higher water content (61 to 64 percent) than the 

 needles (49 to 51 percent), while in the hardwoods the roots contained 

 40 to 46 percent (of fresh weight) and the leaves about 50 percent. 



Gibbs (69, 70, 71) studied the amount and distribution of water in 

 Betula papyri/era Marsh., Populus tremuioides Michx., Pinus bank- 

 siana Lamb., Picea glauca Voss. (syn. P. canadensis B. S. P.), Abies 

 balsamea Mill., and a few other species. He found more marked 

 seasonal changes in the hardwoods than in the softwoods, and these 

 changes, as might be expected, were more pronounced in the sapwood 

 than in the heartwood. Daily changes, with a decrease in he fore- 

 noon and an increase later in the day, were also noted. 



It is interesting to see, however, as is shown in table 1, that the 

 twigs have the highest water content in the more active summer season 

 rather than in the less active winter. 2 



Table 1. — Seasonal water-content percentages in stem and twigs of birch, aspen, 



and pine l 



Month 



Birch 



Stem Twigs 



Aspen 



Stem Twigs 



Pine 



Stem Twigs 



November 

 December _ 

 January.. 

 February. 



March 



June 



July 



August 



September 



Percent 

 41.39 

 42.39 

 45.59 

 46.23 

 44.8 

 38.1 

 41.3 

 39.1 

 38.4 



Percent 

 32.73 

 44.4 

 44.4 

 42.7 

 39.2 

 51.3 

 49.9 

 44.8 



Percent 

 49.1 

 51.0 

 50.0 

 50.5 

 49.6 

 42.2 

 41.6 

 42.7 

 41.3 



Percent 

 33.5 

 49.3 

 47.5 

 50.2 

 46.2 

 50.5 

 50.8 

 53.1 

 46.0 



Percent 

 50.0 

 61.9 

 62.7 

 61.3 

 58.5 

 55.2 

 52.0 

 55.1 

 50.5 



Percent 

 48.3 

 51.2 

 56.1 

 53.7 

 61.3 

 60.1 

 60.2 

 56.6 

 52.3 



i Figures from Tonkel, as reported by Biisgen and Munch (S3, p. 309). 



2 For a history of the development of this subject and the variations in the moisture content of the wood 

 in various parts of the tree and under the influence of various environmental factors, the reader is referred 

 to Biisgen (32). 



