Agriculture Reference
In-Depth Information
nectaries to entice insects with sugary food. Insects
such as bees and flies collect the pollen on their bodies
as they fly in and out and carry it to other flowers.
Petals may have nectar guides, coloured lines to point
the way to the nectaries which may only be visible
to insects. Some flowers are designed to favour
certain insects - for example, in
Antirrhinum majus
(snapdragon) and
Trifolium repens
(clover) the flower
physically prevents entry of smaller non-pollinating
insects and opens only when heavy bees land on it.
Other plant species, such as
Arum italicum
(arum lily),
trap pollinating insects for a period of time to give the
best chance of successful fertilization. The stigmas and
stamens of insect-pollinated flowers tend to be short
and sturdy and the pollen they produce is larger, heavier
and produced in smaller quantities since pollination
success is more likely than in wind-pollinated flowers.
See 'Pollination by Bees' on the companion website.
The seed
Pollination may be followed by fertilization, which is
the fusion of the male sex cells (male gametes) in
the pollen and the female sex cell or ovum (female
gamete) in the ovule to produce a new embryo plant
contained in a seed. The seed itself is formed from
the ovule of the flower and enclosed in the fruit which
is formed from the flower's ovary.
The seed (Figure 8.11), resulting from sexual
reproduction, creates a new generation of plants
that bear characteristics of both parents. The plant
must survive often through conditions that would
be damaging to a growing vegetative organism, so
Figure 8.9
Male cones of
Cedrus atlantica
Glauca
Group (blue cedar)
8
(a)
(b)
(c)
Figure 8.10
Insect pollinated
fl owers are brightly coloured and
sometimes have guidelines in the
petals to guide insects to nectar: (a)
Hemerocallis
(day lily); (b)
Digitalis
stewartii
; (c)
Verbascum
'Cotswold'
