56 FOREST UTILIZATION 



(f) Heartwood and sapwood of conifers are distinguished 

 merely by a difference in color, due to incrustations 

 of rosin in the inner heartwood rings. Pinus echinata 

 has, usually, about thirty sapwood rings. Spruces, firs 

 and hemlocks have no heartwood. Heartwood is con- 

 spicuous in the pines, red and white cedars, lawson 

 cypress, yew, larches and douglas fir. 



B. Chemical qualities of wood. 



I. The walls of the tissue are formed by cellulose (CuHaOn) 



and by lignin (C 8 H 12 O 5 ). 



Cellulose transforms, entirely or partially, in the very year 

 in which the cell is built, by incrustation and reduction into 

 lignin. If a branch or a seedling does not enjoy enough 

 light during summer to allow of thorough lignification, 

 then that branch or seedling is necessarily killed by the 

 winter frost. 



II. Wood and bark contain on an average 45 % (weight) of 

 water. Conifers contain less water than broad-leafed spe- 

 cies. The percentage varies irregularly with the seasons 

 and with the precipitations. 



III. Other substances found in the woody tissue, are: 



(a) In the sap and medulla albumen, starch, sugar, oils. 



(b) In the cell walls tannin, rosin and pigments. 



IV. The specific gravity of pure wood fibre is 1.56. 



C. Outer qualities, or qualities discernible by eye, touch or Fct-nt. 



I. Texture. The ; texture is fine or rough according to the ease 

 with which parts composing the tissue can be distinguished. 

 The texture is : 



(a) Very fine yew, box, holly, persimmon. 



(b) Fine pear tree, hornbeam, black gum. 



(c) Pretty rough spruce, fir, magnolia, cottonwoods. 



(d) Rough cherry, sycamore, maple. 



(e) Very rough oak, elm, locust, beech. 



II Color. Color is an advantage in the furniture trade 

 and a disadvantage in the manufacture of paper. 

 The heart of seasoned wood is always darker than the sap- 

 wood. 



Tropical species are particularly rich in color. 



Wood exposed to air changes its coior^nore or less visibly. 

 The heart of yellow poplar changes to a dark brown. Alder 

 changes from white to red. Ash from white to light violet. 

 Mahogany from brown to black. Walnut similarly. 

 III. Gloss. Gloss is due to evenness, number and size of medul- 

 lary rays. 



Shining species are maple, ash, elm, beech. 



Medium shining are oak, alder, hornbeam. 



Dull are peach, pear, conifers. 



