72 



■Structure of Wood. 



59. Structure of Co 

 niferous Woods. 



and consists of about 44.4 per cent of carbon, 6.2 per cent of hy- 

 drogen, and 49.3 per cent of oxygen. 



256. However plants may differ in form and structure, they are 

 aH the result of cell-growth. These cells form in the interior of 



n pre-existing cells by subdivision, and, by pressing 

 I upon one another, they elongate into fibrous forms, 

 as already shown on page -68. When macerated, 

 these fibers may be separated, and sometimes they 

 afford differences that enable us to determine the 

 class or group to which the woods belong. In the 

 coniferse, there are thin places along the sides of 

 the cells, which can be readily seen under the mi- 

 croscope, and can be found even in the fibers of 

 paper made from wood. 



257. In some woods, as, for eScample, the oak, ash, walnut, etc., 

 the cells grow to a larger size, so as to be visible to the naked eye. 

 These form ducts, which are not continuous for great length, but 

 are intermingled in various fotms, presenting in cross-sections the 

 appearance of pores. They usually contain air, and at certain sea- 

 sons sap. In ascending among these fibers, the sap passes up be- 

 tween and among the fibers, and through their partitions. In some 



of the larger ducts, they have a spiral coil 

 of fiber, or the sides are made up of rings, 

 and they are sometimes marked with dots. 



258. In resinous woods, the turpentine is 

 contained in larger cavities, surrounded by 

 smaller cells. The abundance of this product 

 depends in a great degree upon the vigor 

 of growth, and exposure to the air and light. 



259. The annexed cut shows a section of the 

 linden six years old, enlarged about five di- 

 ameters, in which the concentric layers are 

 distinguished by a somewhat denser and 

 slightly colored line along their outer mar- 

 gin, and their relation to the bark is shown. 

 In this figure, a is the medullary sheath, h 

 the liber or inner bark, d the cellular tissues 

 of the bark, e the pith, and / the epidermis 



0. Section of a Linden Tree „ ^„j.„ i,„ i 



of Six Years' Growth. or outer bark. 



I, 



