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S E L E C T I X C. AND B l' Y I N G SlIT A B L E W O O D

FlC 2.2 A piece of linie wood showing, from the front, the dark outer layer or bark, the pale-brown bast or phloem and the cream-coloured wood or xylem.

weavable fibrę, the bast often looking like part of the bark (Fig 2.2). The wood sends sap up the trec to carry mincrals and water from the ground, and fbod from srorage cclls to make new growth, and to provide some of the ingredienrs for the creation of sugars in the leaf by photosynthcsis. These sugars travel down, being deposited as food Stores in the growing area of the stem. This is the cambium layer, which is the invisible layer of dividing cells between the phloem and the wood. The sugars are then used to create new wood. phloem or bark cells, and some are stored in special storage cells (parenchyma) which we know best as the rays (Fig 2.3).

Thk Grain - Annual Rings

At the beginning of the growing scason larger quantities of sap are sent up the tree. This means that the conducting cells tend to have thinner walls and larger cavities. Later in the ycar the cells havc thicker walls as less sap is needed and sirength is what is required. The rcsult is that in the annual ring so formed there is a change of colour from the early to the late wood and, in

Fic 2.3 Piane wood showing the rays. The figurę on the lefi is typical and is why ąuarter-sawn piane is known as lacewood. The figurę on the right is disturbed, probably by a knot nearby.

some woods (conifcrs particularly) a marked difference in cutting. The eariywood of pine, for instance, is very soft and casily torn, whercas the latewood is dense and cuts crisply (Fig 2.4). Where there is a gentle transition, as in slower-grown sofrwoods and the so-callcd difFusc-porous hardwoods, this problem is not so marked. In tropical timbers the periods of growth arc influenced by rainy seasons which may not even be annual. In many species growth is so even that rings are hard to detect.

Effects of Growth Ring Widths on Carving Propertiks

Ash (Fraxinus excelsio?), oak {Quercus robur and Q. petraea), clm (Ulmus spp) or any other ring-porous timber which has grown fast has a smali proportion of the wood as thin-walled carlywood cells in relation to much denser, fibrous latewood, and is thereforc much harder to carve than slow grown timber. Ash with 6 to 10 rings to 25mm (lin) is good for sports goods and tool handles, but is very difficult to carve when seasoned. Similarly, slow-grown softwoods are easicr to

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