Chemistry of pulp and paper making . Fig. 2. Drawings of Wood-elements 19. TracheidfromTectonagrandis. 20-23. Porlieria hygrometrica. 20. Con-jugate substitute fibres in cross section. 21. Ordinary substitute fibre aftermaceration. 22, 23. Conjugate substitute fibres after maceration. 24-27. Cy-tisus laburnum; elements after maceration. 24. Wood-parenchyma fibre. 26. Substitute fibre. 27. Simple libriform fibre. 28. Cross-sectionthrough cambium and youngest wood of Cytisus laburnum. 29, 30. Mahoniaaquifolium; ducts. 29. After maceration. 30. Longitudinal section.
Chemistry of pulp and paper making . Fig. 2. Drawings of Wood-elements 19. TracheidfromTectonagrandis. 20-23. Porlieria hygrometrica. 20. Con-jugate substitute fibres in cross section. 21. Ordinary substitute fibre aftermaceration. 22, 23. Conjugate substitute fibres after maceration. 24-27. Cy-tisus laburnum; elements after maceration. 24. Wood-parenchyma fibre. 26. Substitute fibre. 27. Simple libriform fibre. 28. Cross-sectionthrough cambium and youngest wood of Cytisus laburnum. 29, 30. Mahoniaaquifolium; ducts. 29. After maceration. 30. Longitudinal section. of ducts separated by maceration from Hieracium. 37-39. Ductsfrom Onopordon acanthiurn. 40. Spirally marked duct from Vitis vinifera. fibre from Jatropha manihot. 48 FIBROUS RAW MATERIALS. Fig. 3. Discoid Markings on Wood Cells Pinus laricio; a. Radial walls; h. A transverse section. Pinus sylvestris; c. Development of markings; d, e. Transverse sections ofnearly perfect and perfect discoid markings. used as a distinguishing characteristic for some woods. Incone-bearing or coniferous trees, such as spruce, fir, hemlock,etc., the wood consists ahnost entirely of tracheids, and whensulphite fibre or ground wood from such trees is examined underthe microscope the discoid markings may be very readily tracheids are generally much longer than the hbriform FIBRE LENGTH 49 fibres from other woods and hence possess greater paper makingvalue. Sap and Heartwood. The sapwood, or that of compara-tively recent growth, is usually lighter in color and containsmore fermentable material than the older and denser heart-wood. Each year a layer of sapwood goes over into heartwoodwhich becomes darker and harder from infiltration of coloringmatters, resins, etc. The sapwood is gene
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