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Culms
Bamboo culms can have an incredible variety
of color and form. Some grow several meters other only few centimeters,
some species have thick culm some thin, some grow erect other bend graciously,
normally they are green in color but can also be brown, yellow, black, reddish,
spotted or striped. All culms have the characteristic structure of
nodes and internodes alternated evenly although there are many exceptions.
For example Phyllostachis aurea often has slanting,
irregular nodes and shortened intenodes in the lower part of the culm. The
'tortoiseshell' bamboo (Phyll. heterocycla 'Kiko'),
which grows in Japan has nodes that are not horizontal but are set at an angle
of 45 degrees in the lower part of the culm. Most bamboo culms are round
but those of Chimonobambusa quadrangularis are
often markedly square in cross section particularly near the base of the culm.
Most species have hollow internodes however
others, like Chusquea, have solid internodes. The culm is
considered the most important part of the plant since so many objects used in
daily life derive from it. One therefore talks of bamboo wood even though in the
strict sense bamboo is not wood. Bamboos do consist of cellulore fibers
but whereas in tree wood these fibers are ausually about one millimeter long in
bamboo they are up to one centimeter long. These long fibers contain
lignin and silica, whereas tree fibers only have lignin.
Culm growth
The shoots appear above the
soil at a specific time of the year, depending on the species. They maybe
as thin as grass or as thick as 25 cm. in diamter, according to species
and age of of the plant. The number of internodes is pre-determined in the
shoot which groes out telescopically at a great speed. when the shoot
emerges from the soil it appears as a series of tight overlapping sheats
surrounding the developing nodes and internodes. They have a protective
function and provide growth hormones. The bamboo shoot groes quickly,
especially in the first week, at the astonishing rate of of several centimeters
per day. Large species in good sites groe as much as 40 cm. per day.
When the elongation period is over the culm sheats dry up and fall off.
These sheats are sometimes attarctively coloured (in certain Phyllostachis
species they are reddish and shiny, in others more or less hairy). In most
genera they fall off straight away, but in some genera like Pseudosasa and
Sasa
they may persist for up to 2 years or longer.
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