Agriculture Reference
In-Depth Information
produce more flowers and fruit than
impoverished buds.
How the riches of the cambium layer are
disbursed determines how well parts of the
plant are nourished. This distribution of
nourishment, and therefore growth, is
determined by plant hormones that are active
in growth points otherwise known as
meristems (pronounced
'merry stems'
).
Hormonesandmeristems(pointsof
growth)
As we all know, hormones are powerful
things. Anyone that has lived with teenagers
knows as much. They govern both the growth
and development in all living things,
including plants. A group of hormones called
auxins
govern which buds get nourished and
produce growth, and which don't. Points of
growth like buds are sites of active cell
division stimulated with auxins (plant
hormones) and are called
meristems
.
Meristems will develop into buds producing
leaves and wood, or flowers and fruit. Every
seed/seedling starts with two meristems - the
radicle
and the
plumule
that give rise to all
other growth points (see Figure 1.3).
Figure 1.2
The cambium layer is made up of vascular
bundles of xylem (dark green) and phloem (light green).
The cambium layer, carrying nutrients up from the roots
(right), and combining these with sugars manufactured by
the leaves (left).
root hairs. The phloem also distributes
sugars manufactured in the leaves to where it
is needed in the plant. Together they
penetrate and sustain all living parts of the
plant. The xylem (pronounced
'zi-lem'
) is in
charge of conducting water from the roots to
the tip of the uppermost leaves - one-way
traffic heading straight up and exiting
through the leaves as water vapour. This
water vapour is why it is often cooler in the
shade of a broad-leaved deciduous tree on a
warm day. The phloem (pronounced
'flow-
em'
) carries sugars manufactured in the
leaves to the whole of the plant, depending
on where the plant needs nourishment. Well-
nourished plants with well-nourished buds
As the plant grows, branching occurs. These
branches/stems emerge from the growth
points, meristems that develop after the
germination stage. Their growth is governed
by the concentrations of the plant hormones
auxin and cytokinin.
These hormones are manufactured in the
meristems (growth points) where plant cells
are rapidly dividing to produce growth. They
are found in the root tips and in buds.
