CHAP. I.] THE PITH. 31 



Willow are somewhat oblique, with the lateral branchlets 

 pendulous and drooping in graceful curves ; in the 

 Lombardy Poplar and Cypress they are nearly erect ; 

 the Oak, in open and exposed situations, takes a wide- 

 spreading form, its branches assuming every imaginable 

 curve; while in the Cedar they are nearly at a right 

 angle. 



The stem is constructed upon the principle of a cone, 

 and consists of a series of perfected layers designated 

 heart-wood, or duramen, while outside these are some 

 young layers that are imperfect, and which are known 

 as the sap-wood, or alburnum ; the exterior is composed 

 of a series of outer layers commonly termed the bark. 

 The main portion of the stem is broadest at the base, 

 and somewhat bell-shaped near the root, but gradually 

 diminishes upwards to the part where the first branches 

 are thrown out, and from this point there is again 

 a still further diminution, until it is finally lost in the 

 extremity of the branchlets. 



The central part of the stem, namely, the pith, is 

 composed of cellular tissue, the cells being very numerous 

 and varying considerably in size, but generally diminish- 

 ing towards the outer edge. The pith is relatively large 

 and full of fluid in the young plant, but does not increase in 

 bulk as the tree grows older ; on the contrary, it appears 

 rather to diminish than otherwise, by the fluid drying out. 

 It retains, however, its place, even in the oldest trees, in 

 the form of a dry mass, often resembling powder, 

 although it is scarcely noticeable in some species on 

 their arrival at maturity. 



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 inside to every board 

 and piece of scantling ; and the careful workman is so 



