Ctdtttral First Principles. 607 



of considerable thickness, and is split by longitudinal furrows, owing 

 to the increasing' diameter of the growincj stem. 



In the inner portion of the cambium are formed the wooJy bundles 

 in a circle round those of the previous season'of growth. In spring- 

 time the cambium forms large but delicate cells, which are easily 

 broken, so that the bark may be stripped easily from the wood 

 More ducts are seen in wood, especially oak, formed at this season 

 than later on, I.e., at the interior of the annual layer. Later on the 

 cells formed in spring become so thickened as bast or wood that the 

 bark cannot be peeled off, and the less active vitality of the tree is 

 marked by the formation of smaller cells. 



The rings of woody bundles when first formed are full of sap, and 

 though growth is confined to the cambium, the passage of sap and 

 deposition of lignine in the cells goes on in the younger layers gene- 

 rally for some years. It is hence called the "alburnum," or sapwood. 

 Mainly from this lignification, but partly also from cohesion, the older 

 or more central portion of the stem becomes much denser, often of a 

 darker colour, and so impassable to sap that it may decay without im- 

 pairing the tree's vigour. The distinction between the sapwood and 

 this " duramen," or heartwood, as it is termed, is well seen in ebony 

 and laburnum. 



In order to show the importance of apparently unpractical matters 

 I make no excuse for quoting the three following paragraphs from 

 " Timber and Timber Trees," the excellent work of a high authority, 

 Mr. Thomas Laslett, of Woolwich : — 



" In the employment of timber in carpentry due regard must always 

 be had to the position of the pith, since there is an outside and an in- 

 side to every board and piece of scantling ; and the careful workman 

 is so well aware of this that he will study to leave, if possible, in any 

 work of construction the outer side only exposed. It is, therefore, 

 necessary in every case to look for the pith or centre of the stem, or, 

 if that has been removed by the conversion of the tree, for the inner- 

 most or oldest layer of heartwood in the plank or board, as that will 

 be the inside of it. If this precaution is disregarded the innermost or 

 earlier layers of wood will lift and shell out after exposure for a 

 time." 



"Timber should be cut as nearly as possible in the direction of the 

 pith rays, the shrinkage in seasoning being, for the most part, angular 

 to them. Workmen in general, and modellers in wood in particular, 

 endeavour to embrace the greatest length of medullary figure in their 

 work to guard against warping. Others, who are engaged in the 

 cleaving of posts, rails, or palings for park and other fences, know that 

 they can only successfully do this by rending the piece in the direc- 

 tion of these rays. It is by a careful study of this that we obtain our 



