102 



TECHNICAL QUALITIES OF THE TREES 



II. Botanical structure of softwoods :- 



(a) The tissue of softwoods is more homogeneous than that of hardwoods. It is mainly formed 

 by tracheae. The ceil wails formed in early spring are thinner and the lumina formed in early 

 spring are larger than those formed in summer. 



(b) Parenchyma is found in the medullary rays and around the rosin ducts. 



(c) Ducts of the form found in hardwoods exist only close to the central pith column. 



(d) The medullary rays are very fine (microscopic), usually only one cell wide and about a dozen cells 

 high. The lowest string of cells in the ray is usually formed by tracheae (exception -red cedar). 



(e) Rosin ducts are not cells merely, but, unlike the ducts of hardwoods, hollow tubes, the walls 

 of which are formed by parenchymatic cells. These ducts are running horizontally as well as 

 vertically in picea, pinus, larix, pseudotsuga. The tissue of the genera abies, taxus, juniperus, 

 thuja, tsuga, libocedrus, cupressus, taxodium, sequoia, chamaecyparis, &c. lacks the ducts. 



(f) Heartwood and sapwood of conifers are distinguished merely by a difference in color, due to 

 incrustations of rosin in the inner (heartwood) rings. Spruces, firs and hemlocks have no heart- 

 wood. Heartwood is conspicuous in the pines, red and white cedars, Lawsons cypress, yew, 

 larch, Douglas fir, &c. 



SOFTWOODS. 



(B) CHEMICAL QUALITIES OF WOOD. 



I. The walls of the tissue are formed by cellulose and by incrustating substances (lignlne). 



Cellulose is C,, Hi,o 0,o, or 12 (C. Hu, 0-,). 



Oxy-cellulose is formed by oxidation, accompanied by the destruction of the organic substance. 



Hydral cellulose is C,,. H,;o O^.,. 



Cellulose treated with nitric acid forms nitro-cellulose. 



