Page 6 - Tài liệu Ebook cây cảnh Bonsai Basics

8 HOW TREES GROW

DEFINITION

Of all plants, trees Jive the longest,
bark thanks to a permanent structure of trunk
and branches, which ensures that the
leaves, flowers and fruits are nourished.
This rigid permanent structure provides
for the tree's long life; it is made of that
particularly resilient substance, wood. A
section cut across the trunk of a tree will
show several zones. These are, starting
from the outer ring and working towards
the centre: the bark, the phloem, the
cambium layer and the true heartwood.
The cambium layer produces the wood
fibres and the vessels which carry sap
upwards to the aerial parts of the tree. As
the tree grows, these vessels become
more numerous, with the new layers
superimposed on the old, which gradu-
ally cease to play an active part in the life
of the tree. In time, they harden to
produce a substance which varies in its
Section of trunk showing the different layers. The
annual growth rings are clearly visible. hardness according to the species: xylem,
or wood. ln this way, the annual life
cycle of the tree produces successive
layers of compressed xylem, clearly visi-
ble in a section of trunk. Each of these
growth rings corresponds to one year in
the life of a tree: so to ascertain the age of
a tree, all you need do is count the rings.
In a well kept bonsai, the production
of cambium is continuous and regular,
as long as the water supply is constant.
But a tree growing in its natural sur-
roundings may have to cope with dram-
atic variations in climate which can
considerably inituence its growth.
Later in this book we shall see that a
major preoccupation of the bonsai en-
thusiast is the thickening of the trunk.
The art lies in allowing the trunk to
thicken while miniaturizing the leaves
and preserving the natural balance of the
tree on a miniature scale. This can only
be achieved by using artifice - wiring,
and pruning the leaves, branches and
Diagram showing how sap circulates. Nutrients and
water taken in through the roots rise within the tree, roots. These methods can produce re-
then sap returns to the roots carrying sugar. markable results.