. Bulletin. Forests and forestry -- United States. Fig. 16 Schematic representation of couilVrona wood .structure: wood of wprucoâ1, natural size; 2, Hmall jiart of one rinj^ majiuilied 100 The vi-rlical tubi's are wood fibers, in this case all " trachcids," 7*1, medullary or ]iith r:iy; /i, transverse traclieids of pith ray; a, &, and r, horth^red pits of the more enlarged. the iniildlc palustris, etc., including most of our " hard '' and " yellow " pines. Section TI. Walls of tracheids of pith ray smooth, without dentate projections, ii. ()ne
. Bulletin. Forests and forestry -- United States. Fig. 16 Schematic representation of couilVrona wood .structure: wood of wprucoâ1, natural size; 2, Hmall jiart of one rinj^ majiuilied 100 The vi-rlical tubi's are wood fibers, in this case all " trachcids," 7*1, medullary or ]iith r:iy; /i, transverse traclieids of pith ray; a, &, and r, horth^red pits of the more enlarged. the iniildlc palustris, etc., including most of our " hard '' and " yellow " pines. Section TI. Walls of tracheids of pith ray smooth, without dentate projections, ii. ()ne or two large pits to each tracheid on the radial walls of each cell of the pith ray.âGroup 3. /'. strohns, laiiilierliiiiiti, and other true white pines. /). Three to six small j>its i>n the radial walls of each cell of the pith ray.âGroup 4. I', parrijana, and other nut pines, includ- ing also /'. ha1ffniriti»a. The general featuies of structure of coniferons woods are represented in the aecompaiiying cut (fig Ki). The structural elements, as in all pine, are few and simple and consist of («) tracheids, the common wood fibers, forming over 90 per cent of the volume; (b) medul- lary or pith rays, minute cell aggregates composed of two kinds of cells, scarcely visible without magnifier and then only on the radial section, yet foniiiiig about 7 to 8 per cent of the volume and weight of the wood in these spe- cies; ((â ) resin ducts, small passages of irregular length surrounded by resin-secreting cells, scattered through the wood, but forming two more or less connected systems, one running in the direction of the fibers, the other at right angles to the first, the individual ducts of the latter system always occupyinj. portion of medullary rays (see PI. XXVII). The tracheitis, or common wood fibers, are alike in all five species, and resemble those of other pines; they are slender tubes, to C mm. (about one- fourth inch) long, forty to one hundred times as lon
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