THE FRUIT – STRUCTURE, TYPES, DISPERSAL OF SEEDS & FEATURES
STRUCTURE OF A FRUIT
What is a fruit? A fruit is a matured fertilized ovary of a flower containing one or more seeds. Contrary to this, some plants do not undergo fertilization for the formation of their fruit. Such fruits are called parthenocarpic fruits e.g. banana and pineapple. Such fruits are seedless.
A typical fruit has the following parts
- The fruit wall called pericarp which is made up of three layers from the inside to the outside (epicarp, mesocarp and endocarp).
- The seed or seeds
- The fruit stalk-the point of attraction between the fruit to the plant.
TYPES OF FRUITS
Fruits are classified based on their origin or structure. Common ways of classifying fruits are
- True and false fruits
- Simple, aggregate and composite fruits
- Fleshy and dry fruits
- Dehiscent and indehiscent fruits
True and false fruit: –
A true fruit develop from a fertilized ovary and it contains a pericarp and seed(s) e. g. mango, cowpea while a false fruit develop from the ovary and other floral parts e. g. apple, cashew.
Simple, aggregate and composite fruits
A simple fruit develops from a single flower with a single ovary e. g. cowpea, maize. An aggregate fruit develops from a single flower with several ovaries (each ovary develops into a fruitlet to form a cluster). The fruitlets have a common fruit stalk e. g. custard apple, strawberry. A composite fruit develops from an inflorescence e. g. fig, breadfruit.
Fleshy and dry fruits
Fleshy fruit is a fruit that has the whole pericarp or at least one of the pericarp thick, soft and succulent is a fleshy fruit. There are six types of fleshy fruits:
- Drupe: – A true, simple fruit with a thin epicarp, fleshy or fibrous mesocarp and a hard and woody endocarp which encloses the seed(s) e. g. mango, coconut, oilpalm fruits.
- Berry: – A true, simple fruit with a thin epicarp and succulent, edible mesocarp and endocarp e. g. tomatoes, guava etc.
- Hesperidium: – A special type of berry in which the epicarp and mesocarp are fused together and the endocarp form distinct chambers filled with succulent hairs e. g. oranges, lemon, grapes etc.
- Pome: – A simple, false fruit in which the fleshy edible part is derived from the receptacle and the core enclosing the seeds from the ovary e. g. apple and pear
- Sorosis: – A composite, false fruit formed from a dense inflorescence e. g. breadfruit, pineapple
- Synconium: – A composite false fruit that develop from a cup-like inflorescence enclosing numerous tiny male and female flowers e. g. fig
Dry fruit is atype of fruit in which the pericarp becomes dry, hard, woody or fibrous when the fruit ripens. Dry fruits can be grouped into dehiscent or indehiscent fruits
Dehiscent fruits split open to release the seeds when ripe. Four main types are
- Legumes: – The pericarp split open longitudinally along both side to release the seeds e. g. cowpea. Flamboyant etc.
- Follicle: – The pericarp split open longitudinally on one side only to release the seeds e. g. silk cotton, kola
- Capsule: – The pericarp slit along many sides to release the seeds e. g. okro, cotton etc
- Schizocarp: – Breaks up into units enclosing one seed each e. g. desmodium, cassia etc.
Indehiscent fruits fall to the ground when ripe, eventually decayed to release the seeds. Five main types are
- Achene e. g. clematis
- Cypsela e. g. tridax, sunflower, marigold
- Caryopsis e. g. maize, rice
- Nut e. g. cashew nut
- Samara e. g. combretum
DISPERSAL OF SEEDS AND FRUITS
This is the transfer of the seed or fruit from the parent plant to other places where such seed may germinate. The essence of dispersal includes the following:
- To avoid undue competition for nutrients ,light space and water
- To prevent overcrowding of plants
- To prevent spread of disease
- To encourage colonization of new area for such plants
Agents of dispersal
These are the means by which seeds and fruits are removed from parents to other places. These agents include:
- animals and man
- explosive mechanism
Features that aids methods of dispersal
- WIND – (i) Fruits or seeds are light. (ii) Fruits or seeds may have floss, tuff or pappus e. g. tridax, cotton, combretum etc.
- WATER – (i) Light fruits or seeds that can float in water (ii) Waterproof epicarp (iii) Fibrous mesocarp that can trap air to keep it afloat e. g. coconut
- ANIMALS AND MAN: – (i) The fruits or seeds may have hooks or hairs to attach to the animal skin (ii) The fruits are edible and the seeds indigestible e. g. pepper, desmodium
- EXPLOSIVE MECHANISM: – (i) Presence of one or more lines of fission or weakness e. g. cowpea, flamboyant, okro etc.
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