Flower structure
The flower structure is shown in Figure 7.4.
The flower is initially protected inside a flower bud by the calyx or ring of sepals, which are often green and can therefore photosynthesize. The development of the flower parts requires large energy expenditure by the
- SM
Petal (corolla)
Anther Filament
Stigma Style Ovary Ovule Sepal (calyx) Receptacle Pedicel
Petal (corolla)
Anther Filament
Stamen -male organ
Female organ
Stigma Style Ovary Ovule Sepal (calyx) Receptacle Pedicel
Figure 7.4 Flower structure, e.g. (a) flower of Glaucium corniculatumand (b) diagram of typical flower to show structures involved in the process of sexual reproduction
- Figure 7.5 Tulip 'Attila', e.g. of tepals - outer layers of flower are similar
A plant possessing flowers with both male and female organs is hermaphrodite.
Species with separate male and female flowers on the same plant are monoecious.
Species which produce male and female flowers on different plants are dioecious.
plant, and therefore vegetative activities decrease. The corolla or ring of petals may be small and insignificant in wind-pollinated flowers, e.g. grasses (see p134), or large and colourful in insect-pollinated species (see p135). The colour and size of petals can be improved in cultivated plants by breeding, and may also involve the multiplication of the petals or petalody, when fewer male organs are produced.
The flower may include other parts:
- Tepals, where the outer layers of the flower have a similar appearance, making the sepals and petals indistinguishable. They are common in monocotyledons such as tulips (see Figure 7.5) and lilies.
- Androecium, the male organ, consists of a stamen which bears an anther that produces and discharges the pollen grains.
- Gynaecium, the female organ, is positioned in the centre of the flower and consists of an ovary containing one or more ovules (egg cells). The style leads from the ovary to a stigma at its top where pollen is captured.
- The flower parts are positioned on the receptacle, which is at the tip of the pedicel (flower stalk).
- Nectaries may develop on the receptacle, at the base of the petals; these have a secretory function, producing substances such as nectar which attract pollinating organisms.
- Associated with the flower head or inflorescence are leaf-like structures called bracts, which can sometimes assume the function of insect attraction, e.g. in Poinsettia.
The flowers of many species have both male and female organs (hermaphrodite), but some have separate male and female flowers (monoecious), e.g. Cucurbita, walnut, birch (Betula), whereas others produce male and female flowers on different plants (dioecious), e.g. holly, willows, Skimmia japonica and Ginkgo biloba.
Average user rating: 5 stars out of 2 votes
Post a comment