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The
texture of the wood is fairly even with a moderately straight
and slightly interlocking grain. It is whitish yellow when
freshly cut, but the wood turns to light brown during drying.
At this stage latex vessels can be found with a characteristic
smell in some parts of the wood. The wood is soft to moderately
hard with an average weight of 515 kg m-3 at 12% moisture
content. Pores on the cross section are diffused and of medium
to large size, mostly solitary, but sometimes in short multiples
of two to three, filled with tyloses. Vessel tissues are conspicuous
in radial and tangential faces and are of the order of about
200 u in diameter. Wood parenchyma are abundantly visible
to the naked eye appearing as narrow. irregular and somewhat
closely spaced bands forming a net like pattern with rays.
The rays of the wood are moderately broad, rather few and
fairly widespread. The pits found between the vessels and
rays are half-bordered with narrow width. The length of the
fibres is more than 1.0 mm on the average and the width is
about 22 : when dry. The cell wall thickness when dry is about
2.8 :. The other characteristics of rubber wood are summarised
in Table 2 (Bhatt et al. 1984). These authors further studied
the variation in the properties of the wood and bark at different
heights and came to the conclusion that there is no significant
variation of bole quality between height levels of a tree
or between trees in a plantation, in contrast with naturally
grown trees in a forest.
There is insignificant heart wood formation and no transition
appears between sapwood and heart wood, which is confined
near the pith only. Growth rings or annual rings are not
visible in rubber wood, unlike many other woods (ring porous
woods). However, concentric false rings sometimes appear
on the wood, depending on the presence of tension wood (g~latinous
cells) which are fairly common in most of the clones. Maximum
number of such rings are found in the basal portions with
decreasing number towards the top. The tension wood may
vary from 15 to 65%. and such erratic distribution tends
to give a woolly appearance on the surface of wood. Such
distribution and variation are supposed to be responsible
for some of the commonly observed defects that may occur
during drying and processing.
There are very few natural defects in rubberwood capable
of making it unsuitable for general purpose applications.
Unlike typical forest based trees, rubberwood is grown on
plantations where the trees are carefully nurtured. However,
due to the presence of growth stresses and induced drying
stresses, a few defects such as splits, cracks and checks
are usually observed. These can be avoided or minimised
by careful control measures during storage and drying. Decay
or rot often occurs in rubber wood due to attack by fungi,
which can be avoided by suitable chemical treatments. Similar
defects due to other biological agencies like insects and
birds or due to weather can also be suitably minimised by
chemical treatments. Other defects, like grain orientation,
knots, woolly surfaces etc., can be lessened by suitable
machining and sorting. Logging defects like ruptured or
crushed fibres can be eliminated by employing proper tools
and observing necessary precautions while logging and transporting.
Thus the defects that are commonly observed in rubberwood
are not so serious as to render it useless.
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