Agriculture Reference
In-Depth Information
(Fig. 11.3). Although there are occasional lines or cultivars that produce an
abundance of lateral branches, especially during the juvenile period, the main
stem normally grows without branching, unless the growing point is injured.
Natural growth of the axillary branches does occur when the trees become
3-5 years old. The stem is semi-woody and hollow and a major site of starch
storage. The bark is smooth, greyish in colour, with large, prominent leaf
scars. When the stem is wounded, a thin milky sap oozes from the wound.
After transplanting, shoot growth is initially slow, though considerable
root growth is taking place, extending out well beyond the canopy drip line.
Stem growth is then rapid up to fl owering, increasing in circumference up
to 2 mm per day. Growth rate peaks at fl owering then declines as the tree
starts bearing (Fig. 11.4). The rate of growth is infl uenced by nitrogen and
phosphorus supply, irrigation and temperature.
Leaves
A cluster of leaves occurs at the apex of the plant and along the upper part
of the stem and makes up the foliage of the tree. New leaves are constantly
formed at the apex and old leaves senesce and fall. Leaves are palmately lobed
with prominent veination and can measure 40-50 cm or more in diameter
and have an individual leaf area of 1625 cm
2
, with
ca
15 mature leaves per
plant (Fig. 11.5). In the tropics, new leaves appear at a rate of two to three
a week (Chan and Toh, 1984); in Hawaii the rate is 2.4 per week during the
cool season and up to 3.0 in the warm season. Petioles are cylindrical, hollow
and 60-90 cm long, depending upon the cultivar. The most recently matured
leaf 's fresh weight (~10th leaf from 2.4 cm juvenile leaf) can vary from
ca
50
to 170 g. The leaf petiole dry mass increases at a rapid rate until fl owering
then increases more slowly, peaking after fruit bearing starts (Fig. 11.5).
In
fl
orescence and
fl
owers
There are three primary groups of fl owers, i.e.
pistillate, staminate and
hermaphrodite, with many variants, especially in the hermaphrodite group
(Fig. 11.3). Flowers are borne on modifi ed cymose infl orescences that appear
in the axils of the leaves. The type of infl orescence depends upon the sex of
the tree. The pistillate tree produces only pistillate fl owers on short, 4-6 cm
peduncles, with a functional pistil devoid of stamens (Fig. 11.3a). The fi ve
petals are separate but are inconspicuously fused together at the very base of
the ovary. In staminate trees, fl owers are sessile and are produced in clusters
on long, pendulant racemes 60-90 cm long. The individual fl ower is tubular
with ten stamens in two series of fi ve, attached to the throat of the corolla
tube, and lacks an ovary. The hermaphroditic form (Fig. 11.3b) is between the
