184 Transactions.—Miscellaneous. 
Art. X.—The Building Materials of Otago. By Wurm N. Bram, C.E. 
[Read before the Otago Institute, 31st October, 1876.] 
TIMBERS. 
Properties of Timbers. 
Although the properties of timbers generally are better known than 
those of the other building materials that have already been discussed, it is 
necessary for the proper investigation of our subject to consider the leading 
characteristics that bear on their economic value, and in doing so I shall 
trace the timber through the various stages of its existence. 
Structure.—As you are probably aware, the structure of ordinary timber 
is, to all intents and purposes, identical with that of a brick wall: it is 
composed of vertical and horizontal layers, breaking joints, and cemented 
together in much the same way. Tbe vertical joints, consisting of the 
annual rings and medulláry rays, are quite clear and distinct; but the 
horizontal ones, made from the interlacing of bundles of woody fibre of 
irregular lengths, are only visible to the microscopist. It is this difference 
in the length of the scarf, or joint, that makes splitting timber so much 
easier than cutting it across the grain. The concentric rings represent the 
growth in a year or season ; they are generally very distinct in timber 
grown in a cold climate, where there is a decided period of repose in the 
the vegetation ; but in many tropical trees the rings are scarcely discern- 
able, and some botanists allege that occasionally so many as four rings are 
formed in one year. The medullary rays are thin plates of woody matter 
that radiate from the pith to the bark, and form the weft which interlaces 
with the warp of the annual rings. Although believed to exist in all 
timbers, these rays cannot be traced in the firs and pines of the old country, 
but are very conspicuous in oak, beech, and other hard woods; this rule 
does not hold good in Otago, for there are few timbers hard or soft in 
which they do not appear. These medullary rays are what give the peculiar 
watered figure called silver grain, which is so much prized by cabinet- 
makers and other manufacturers of fancy wood-work. 
Growth.—The principal agent in the formation and development of 
woody fibre and tissue is the sap, which performs the same functions in 
plants that blood does in animals. After being extracted by the roots from 
the soil, it rises through the trunk to the leaves, and is there subjected to 
certain chemical changes that fit it for the formation of timber. In saplings, 
the fluid permeates and rises through the whole trunk ; but in old trees 
with solid heart-wood, it is confined to the sap-wood and the bark. At this 
stage the heart-wood contributes nothing to the other parts of the tree 
