. Canadian forest industries January-June 1923. Lumbering; Forests and forestry; Forest products; Wood-pulp industry; Wood-using industries. Fig. 3—Transverse sections of Douglas fir (magnified) slow, medium and fast growth of summerwood, has a greater per cent, of its area occupied by sum- merwood than the fast-growth section. The section with narrowest rings however, although its summerwood bands are the most num- erous of the three, has the least total area of summer-wood. It is a general rule for those softwoods which possess heavy summerwood that fast-growth timber has only a small per ce
. Canadian forest industries January-June 1923. Lumbering; Forests and forestry; Forest products; Wood-pulp industry; Wood-using industries. Fig. 3—Transverse sections of Douglas fir (magnified) slow, medium and fast growth of summerwood, has a greater per cent, of its area occupied by sum- merwood than the fast-growth section. The section with narrowest rings however, although its summerwood bands are the most num- erous of the three, has the least total area of summer-wood. It is a general rule for those softwoods which possess heavy summerwood that fast-growth timber has only a small per cent, of summerwood, medium-growth timber the maximum amount and very slow growing timber an amount which is less than the maxi- mum achieved by medium growth. Summerwood Gives Strength to Timber The importance of summerwood in softwoods may be better ap- preciated if it is realised that the bands of thick-walled fibres add much more weight and strength, to the timber than the relatively thin-Availed fibres of the springwood. Fig. 4 demonstrates the effect of summerwood-content upon the weight of the timber. The specific gravity of a shipment of representative Douglas fir (Pseudotsuga 0-42 <H0 Dit 016. 0J4 0-J2 0*0 0 0-02 . 0 Sped Ft, fit airily in r ofD xjgbs to rat Fir 6_o£flI twfh. 1 nu»t pmucrs L»liimau or cwu Rings per inch. Fig. 4—Relation of specific gravity to rate of growth in Douglas fir mucronata) from the Pacific Coast is plotted graphically against the groAvth-rate (rings per inch). The curve shows what the photographs demonstrated, namely, that Douglas fir of medium growth-rate, with the greatest propor- tion of summerwood, is heaviest; and that extremely fast or slow- growth timber, having less summerwood, is consequently lighter. The tests whose results are embodied in these curves, were made by the Division of Timber Tests at the Forest Products Laboratories of Canada, Montreal, in the course of their work of testing Canadian timbers. It has long been r
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectforests, bookyear1923
