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Rhizomes
Rhizomes are underground stems which grow
and branch away from the bamboo plant, thus enabling new territory to be
colonized. Each year, culms arise from the rhizomes to form the aerial
parts of the bamboo. These rhizomes are often so tightly packed that the
soil under a bamboo plant seems to be filled with them. They form a
perfectly compact layer roughly 1 meter (3 feet) under the ground.
The growing point of a rhizome is very
hard, allowing it to penetrate into the surrounding soil; often it's strong
enough to break barriers and travel underground for several meters.
The true roots of a bamboo develop from the
nodes of a rhizome, to supply the bamboo with water and nutrients. Roots
emerge from the node ring, are thinner than the rhizome and are not
segmented.
Rhizomes can be broadly divided into two
growth types: pachymorph (sympodial) and leptomorph (monopodial). The
habit of the bamboo grove above the ground is dependent upon the rhizome type,
which also determine whether the grove will be invasive or clump forming and it
also determines the distances between individual culms.
Pachymorph
rhizomes are typical of tropical
bamboos (i.e. genus Bambusa), although also occurr in some temperate
bamboos. The rhizomes are short and thick, curved upwards. The
internodes are very short and look compressed. Above ground, the culms grow
close together in a tight clump which expands evenly round its circumference
only moving a short distance each year.
Leptomorph
rhizomes are characteristic of bamboos growing in temperate regions and
include genera such as Phyllostachys and Pleioblastus. These
rhizomes are long and thin, growing horizontally over considerable
distances. Differently from pachimorph rhizomes, both new rhizomes or
culms can develop from the dormant buds on the nodes. The culms are
thicker than the rhizome from which they have developed. Bamboos with
monopodial rhizome produce a more open clump structure where the culms have a
much greater spacing, often in a straight line away from the mother clump.
These bamboos are invasive and can travel sitances and overcome obstacles.
It shopuld be noted that many species do
not exactly follow in any of the two categories of rhizoms. These
intermediate rhizomes structure are typical of the high altitude bamboos where
extreme growing condition affect growth behavior, one example is Arundinaria
anceps.
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