A Chapter On Oaks.

A CHAPTER ON OAKS .

BY BKO . K . M . BANCROFT Member of the Civil and Mechanical Engineers' Society . Trees under these circumstances become exposed to the inconvenience of what are called star-shakes , or cracks in the body of the wood , radiating from the centre towards

the ' circumference , with the greatest width towards the centre , whereas the star-shakes or cracks of young timber have their widest openings towards the circumferences . Mr . Burnell in a paper read before the Society of Arts , says , if the trees thus affected should be allowed to stand , the heartwood will , in the end , entirely decay , and the stem Avill become hollow , especially if a large branch should be broken off , and thus allow external moisture access to the inner wood through the ruptured fibres . It follows from

these conditions , that wood intended to be used in the more important operations of building , should be obtained from trees which had not exceeded their age of growth ; and it also appears that the season of the year when the trees are felled , has a distinct influence upon the durability of the wood . Theoretically , the best period for that operation would be the one immediately preceding the first movements of the sap in spring time ; but as it is not possible , in practice , to command the amount of labour required for such purposes , it is customary to fell the timber of regularly worked forests during the whole of the season comprised between the moment vegetation ceases in the autumn , and the moment when it commences in the spring—in other words , it is

customary to fell timber of the best description between the months of October and April , in our latitudes at least . There are some other conditions in the growth of trees which give rise to the defects it may be desirable to notice here . Thus , in the very heart of sound , healthy-looking trees , it is by no means rare to meet with circular bands , which form separations , in fact , between the layers of wood , aud which are supposed to be occasioned by the action of violent winds upon the stem of the tree at the period of the formation of the new layers .

These cup-shakes , as they are called , are most fequently to be met near the roots of trees ; and if they should be black and accompaineel by star-shakes , they maternity affect the strength of the timber , though they do not seem to have much influence on its durability . Sometimes the cup-shakes exhibit themselves externally by an abnormal increase of bulk of the stem a little above the root . In other trees , again , circular bands occurin which the wood is of a softer and more spongy character than on the rest of the tree

, , and which even occasionally present a commencement of decay . This accident occurs in the very best timber , and , unfortunately , whenit does so occur , the effect seemsto make itself felt through the whole length of the tree . —a circumstance by no means extraordinary if the generally received opinion as to the cause of the phenomenon be correct , viz ., that it is produced by the action of sharp frost upon the rising sap in the newly-formed layers of wood .

Timber which possesses this character will infallibly decay in buildings , and it should therefore be carefully excluded ; and great hesitation may also be admitted as to the use of timber which presents large bands of what are supposed to be indefinitely marked annual growth , because the existence of zones of wood so affected may be considered to indicate that the tree was not in a healthy state when they were formed , and that the wood then secreted lacked some of the elements required for its durability , upon being subsequentl y exposed to the ordinary causes of decay .

There are two kinds of this timber common in England and America . Oak of good qualit y is more durable than any other wood which attains the same size . Its colour is a well known light brown , which darkens with age . Oak is a most valuable wood for shi pbuilding , carpentry , and works requiring great strength or exposed to the weather . IJ is also much used for carved ornaments , panelling of rooms , pulpits , stalls and standards for churches . It is likewise used in the construction of all kinds of buildings for