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 that of the lime; those are difficult which are hard and have many knots and a compact and twisted grain. The most difficult woods are those of aria (holm-oak) and oak, and the knotty parts of the fir and silver-fir. The softer part of any given tree is always better than the harder, since it is fleshier: and carpenters can thus at once mark the parts suitable for planks. Inferior iron tools can cut hard wood better than soft: for on soft wood tools lose their edge, as was said in speaking of the lime, while hard woods actually sharpen it: wherefore cobblers make their strops of wild pear.

Carpenters say that all woods have a core, but that it is most plainly seen in the silver-fir, in which one can detect a sort of bark-like character in the rings. In olive box and such woods this is not so obvious; wherefore they say that box and olive lack this tendency; for that these woods are less apt to 'draw' than any others. 'Drawing' is the closing in of the wood as the core is disturbed. For since the core remains alive, it appears, for a long time, it is always removed from any article whatever made of this wood, but especially from doors, so that they may not warp : and that is why the wood is split.

It might seem strange that in 'round' timber the core does no harm and so is left undisturbed, while in wood whose texture has been interfered with, unless it is taken out altogether, it causes