Page 163 - Biology_F5

Biology for Advanced Level Secondary Schools

some have a single carpel or a number of the ovary bear a peculiar characteristic
separate carpels, or a number of carpels of angiosperms. They contain an embryo
fused in a variety of ways. The carpel is sac in which the female gametophyte is
either single or united in a closed hollow found. The distal end of the ovary bears a
housing (ovary), with one or more ovules. prolonged structure known as style, which
The ovules which are enclosed within terminates in a sticky surface called stigma.
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Stigma Anther
Androecium
Carpel Style Filament

Ovary Petal

Receptacle Sepal

Pedicel

Figure 3.32: A generalised longitudinal section of an angiosperm flower

Flowers have the basic parts mentioned both gynoecium and androecium parts,
above, but morphological variations while others have only one part.
are common across plant species. These
variations are based on the following Position of floral whorls on receptacle
attributes: As pointed out earlier, the position of floral
(a) The manner of insertion of the parts. parts on the receptacle varies across the
(b) The number of floral parts: Some species. Based on the arrangement of the
flowers have all four whorls while floral leaves on the receptacle in relation
others have less than four whorls. to the position of the ovary, three types of
(c) The freedom or fusion of floral parts: flowers are recognised:
Some parts in some flowers may be
fused, while other parts may not. (a) Hypogynous flower
(d) The relative position of the floral parts In this flower, the calyx, corolla, and
androecium arise from the lower position
on the receptacle; may be above or of the ovary. This means that the calyx,
below the receptacle. corolla and androecium are inserted below
(e) The symmetry of the flower: some the ovary, that is the ovary is positioned
flowers have radial or bilateral above them. The ovary is therefore said
symmetry, while others are to be superior, as it occupies the highest
asymmetrical. position in the receptacle (Figure 3.33).
(f) The distribution of the sexual parts Examples of hypogynous flowers include
within the flower: Some flowers have Hibiscus, tulip and tomato flowers.

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