Geoff' s Woodwork for Students of Woodwork
Timber growth
Cross section of a tree truck Annual or growth rings ~ in temperate climates there are two distinctive growth seasons, spring and summer ~ the spring growth is rapid and is shown as a broad band whereas the hotter, dryer summer growth shows up narrow. In tropical countries the growth rings are more even and difficult to distinguish.
Bark ~ the outer layer, corklike and provides protection to the tree from knocks and other damage. Bast ~ the inner bark, carries enriched sap from the leaves to the cells where growth takes place. Cambium ~ layer of living cells between the bast and the sapwood. Crown ~ the branches and leaves that provides its typical summer shape. Heartwood ~ mature timber, no longer carries sap, the heart of the tree, provides the strength of the tree. Usually a distinctive darker colour than the sapwood.
Medulla ray ~ (rays) food storage cells radiating from the medulla ~ provides a decorative feature found in quarter cut timber. Pith or medulla ~ the centre of the tree, soft and pithy especially in the branches. Sapwood ~ new growth, carries the raw sap up to the leaves. Usually lighter in colour than the heartwood, especially in softwoods. Trunk ~ main structure of the tree, produces the commercial timber. Root structure  ~ Absorbs water and minerals from the soil.  It is the anchor of the treee.
Hardwoods and Softwoods.
There are two main groups of timber producing trees used commercially; softwoods and hardwoods. These terms immediately create contention because they do not accurately describe the timber correctly. Softwoods.  Softwoods are coniferous trees and the timber is not necessarily 'soft'. They are 'evergreen'. (The larch is an exception) Their general characteristics are: Straight, round but slender, tapering trunk. The crown is narrow and rises to a point. It has needle like or scale-like shaped leaves and it's fruit, i.e. it's seeds are carried in cones. The bark is course and thick and softwoods are evergreen and as such do not shed their leaves in autumn. Hardwoods. Hardwood trees are broadleaf and generally deciduous. Their timber is not necessarily hard. For instance, balsa (the timber used for making model planes) is a hardwood. The general characteristics are: Stout base that scarcely tapers but divides into branches to form a wide, round crown. The leaves are broad and may have single or multi lobes. The bark may be smooth or course and varies in thickness and colours. Its fruit may be: nuts, winged fruits, pods, berries, or fleshy fruits.
Other terms (  ** I am afraid there are often contradictory explanations in some terms. UK readers especially be aware of the n.american term of 'burl' in examinations) Branch ~ main bough from trunk Bole ~ The greater part of the trunk under the first branch. Boulle (log) ~ french term for through and through cutting of the trunk and retained complete in the seasoning process especially for matching grain. (included for interest only) Bur(r) (burl n.americ.) ~ produced by the tree to form over early growth of twigs known as epicormic shoots.  Also formed to protect damaged timber. Provides beautiful figure prized by cabinet makers and for making veneers. Burl ** ~ (buttress)    Briar pipes are made from this material nearer the root structure.  I believe North American usage includes the description similar to burr. Butt (butt-swell) ~ The wider part of the trunk especially close to the ground.  Veneers have some 'burry' circles but is characterised by a wild freakish pattern. Buttress ~ On some trees the  widening  of the bole providing interesting grain especially for veneers. The part of the trunk or bole as it enters the ground.   Large tropical trees have 'butresses' reaching well over a metre from the ground. Crotch ~ the forked meeting of the trunk with a branch forming interesting growth ring formation. Trunk ~ stem ~ main part of tree ~ see bole
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17th April 2004