FOREST UTILIZATION 



55 



large pores, or else "diffuse porous," if the ducts are 

 evenly distributed over the entire ring. Sapwood. 

 and heartwood are merely distinguished by a differ- 

 ence of color, caused by incrustations of pigments,, 

 lignin, tannin etc., in the walls of rings formed a 

 number of years before. The number of years elaps- 

 ing before incrustation takes place is small in catalpa,. 

 chestnut, locust ; and larger in yellow poplar, white 

 oak, walnut where it is about thirty or forty years 

 old. Beech, maple, basswood etc. do not form any 

 heartwood. 



Medullary 

 Rays. 



Scarcely 

 visible. 



Ringporoue 

 always with 



f Castanea 



I Roblnia 



J Fraxinus 



I Hicoria 



Ulmus 

 Morns 

 Ailanthus 



Quercua 



Vitis 



Rosa 



GENERIC STRUCTURE OF HARDWOODS. 



Diffuse porous. 

 Inner pores 

 more numer- Pores absolutely even 



ous, always With heart. Without heart, 



with heart. 



Rhamnus .Tuglans Aliius 



Rhus Pyrus malus . Pyrus communla 



Syriuga Sorbus Crataegus 



Sails Betula 



Liriodendron Aesculus 



Populus 



Prunus Tllia 



Acer 

 Corylus 

 Carplnus 

 Ilex 



Sambucns Platanus 



Fagus 



II. Botanical structure of softwoods. 



(a) The tissue of softwoods is more homogeneous than that 



of hardwoods. It is mainly formed by tracheae. 

 The cell walls formed in early spring are thinner and 

 the lumina formed in early spring are larger than those 

 forrhed 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 run- 

 ning horizontally as well as vertically in picea, pinus, 

 larix, pseudotsuga. 



The tissue of the genera abies, taxus, juniperus, thuja, 

 tsuga, chamaecyparis etc. lacks the ducts. 



