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.

Fruits are enjoyed by many different animals, but they serve an important function for plants. A fruit is the mature ovary of a flower. Fruits protect seeds and aid in seed dispersal.  

Fertilization triggers hormonal changes that initiate the transformation of the ovary into fruit. In the absence of fertilization, flowers generally wither and do not develop into fruit. 

In seed-bearing plants, the structure that gives rise to female reproductive cells is called the ovule. The ovules usually develop into seeds as the ovary wall develops into the pericarp. 

In a typical fleshy fruit, the pericarp consists of three layers. The outer layer is called the epicarp, the edible middle portion is the mesocarp, and the innermost hard seed covering is the endocarp. 

In some fruits, such as pea pods, the pericarp is dry at maturity. In other fruits, such as peaches, the pericarp remains fleshy. 

Fruits can be categorized according to how they develop from carpels—the ovule-bearing parts of flowers. A fruit formed from one carpel, or fused carpels of a single flower ovary, is called a simple fruit. 

An aggregate fruit, by contrast, develops from multiple separate carpels of a single flower. A multiple fruit, on the other hand, is formed from the many carpels of the multiple flowers that make up an inflorescence. 

In accessory fruits, such as pears, organs other than the ovary largely contribute to fruit formation. 

Overall, a mature fruit allows a plant to propagate by protecting its seeds from environmental stressors and aiding in their dispersal.