44
THE ESSEX NATURALIST.
yields an extremely durable timber, with the valuable property
of withstanding alternate wet and dry conditions ; it is some-
times used for piles, and it is said that many of the piles on which
Venice is built are of this wood.
Hardwoods. Of the hardwoods the Oak (Quercus Robur
and Q. sessiliflora) is pre-eminent : that grown in forests
yields straight timber in fairly long pieces, but isolated trees,
growing in open situations, usually have a short bole and tor-
tuous branches ; these crooked branches were of great value to
shipwrights for the building of wooden ships, and were more
highly prized than pieces which had been bent artificially. The
wood is extremely durable, as is shown by the following data
taken from Howard :—The ship "Royal William" was built
in 1715-9 and broken up after 94 years service ; beams of the
roof of Westminster Hall, erected in 1399, were not repaired until
more than 500 years later ; sound English oak was taken from the
foundations of a Hull church, built about 1270. Often the wood
is very ornamental, showing a beautiful silver grain caused by
the large rays : in some trees the heartwood is a rich reddish
brown colour, and is known as brown oak ; such trees are of
sporadic occurrence. Brown oak is now known to be produced
by certain fungi. Another fungus (Chlorosplenium aeruginosum)
turns the wood a green colour, such wood is familiar in the
well known Tonbridge ware. As might be expected from the
size of the rays, oak cleaves easily in a radial direction ; cleft
oak is used among other things for barrel staves and for palings.
An interesting feature in the making of barrels is the use of
the American Red and White Oaks for the purpose. Generally
the White Oaks have the vessels stopped up with tyloses, and can
be used for tight cooperage : Red Oaks, however, usually have
the vessels free from tyloses and in consequence cannot be used
for the staves of barrels intended for liquids, otherwise leakage
would occur. The hard heavy wood of the False Acacia (Robinia
Pseudacacia) is also characterised by the abundance of tyloses
in the vessels ; like oak it is an extremely durable wood, and it
is not improbable that the sealing of the vessels by tyloses may
account for its durability in preventing fungus spores from
finding lodgement in the vessels. Ash (Fraxinus excelsior) also
furnishes a tough durable wood, which differs from that of oak,
amongst other features, in its elasticity. For this reason it