35.4: Fruit Development, Structure, and Function
Fruits form from a mature flower ovary. As seeds develop from the ovules contained within, the ovary wall undergoes a series of complex changes to form fruit. In some fruits, such as soybeans, the ovary wall dries; in other fruits, such as grapes, it remains fleshy. In some cases, organs other than the ovary contribute to fruit formation; such fruits are called accessory fruits.
Fruits can be classified based on the number of flowers and the structure of the carpels involved in their formation. Fruit that develops from a single flower with one carpel or multiple, fused carpels are classed as simple fruits. Aggregate fruits develop from multiple, separate carpels of a single flower. In contrast, multiple fruits are produced when multiple carpels of many flowers that make up an inflorescence combine to form a single fruit.
Fruits help protect and disperse a plant’s seeds. Many fruits depend on biotic factors, such as fruit-eating animals, to disperse seeds. Undigested seeds in fruit can be remotely dispersed in animal droppings. Other fruits rely on abiotic factors, such as water and wind, to disperse seeds. Some fruits can even disperse themselves - for example, mature pea pods explode and release seeds.
Water-dispersed seeds often have light, buoyant fruit. For example, coconuts float and have hard exteriors, and their seeds can still germinate after several months afloat at sea. Maple seeds, on the other hand, are dispersed by wind. Maples have winged fruit that spins like a helicopter, facilitating remote dispersal.
The development of seed-containing fruit relies upon fertilization. Unfertilized flowers generally do not develop into fruit. Once fertilized, seeds can remain dormant for months, years, or even decades, until conditions become favorable for germination.