. Australian Garden and Field. THJ^; CJARDEN AND FIELD. Norember, 1913 The Practical Use of Timber. Although the following notes refer more particularlv to western (N'.) timbers, the principles enunciated applv nevertheless equally to the use of timbers from other districts. Before entering upon the subject we will give an ek^mentarv description of the struc- ture of timber. All trees that provide us with timber are outward growing trees âthat is to say, they increase in girth by developing successive layers round the trunk next to the bark. Each year gerterallv adds one of the layers or r
. Australian Garden and Field. THJ^; CJARDEN AND FIELD. Norember, 1913 The Practical Use of Timber. Although the following notes refer more particularlv to western (N'.) timbers, the principles enunciated applv nevertheless equally to the use of timbers from other districts. Before entering upon the subject we will give an ek^mentarv description of the struc- ture of timber. All trees that provide us with timber are outward growing trees âthat is to say, they increase in girth by developing successive layers round the trunk next to the bark. Each year gerterallv adds one of the layers or rings, and consequently thev are called " annual ; In addition to the annual rings, trees have me- dullary rays, which are thin and generally broken lines, radiating from, the centre, or pith, to the bark, and \-ice \*ersa. ' These rays are not ver}' apparent in some tree's, but in dry express pine they are easily se>zn. Cabinet m-akers call these rays the "silver ; The trunks and branches of trees consist of two kinds of woodâthe hard, dead heartwood, or dura, men, and the soft sapwood, or al- burnum. The latter is much lighter in colour than the former. The bark consists of an outer and inner layer. It is through the sapwood that the root-sap is carried up to the leaves. Here 'chemical changes take place with the carbon that has been abstracted from the car- bon dioxide of the air, which has found its wav into the leaves by means of the breathino- pores or stomata. After the various changes have taken place the " food sap " returns by means of the inner bark and passes through the medullary ravs to noiirish the tree. Heartwood is much stronger and more durable than sapwood, and the oxvter portion of the heart- wood is stronger than that near the centre, or pith, more particu- larlv if the wood is " pipev," be- cause then it has been subjected to decav and is very brittle. Old wood is stronger, thouijh lighter, than voung
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