Fruit Formation

As the ovule inside the ovary is transformed into the seed by the post-fertilisation events

described above, the surrounding ovary wall itself develops in parallel, maturing into the fruit

that will enclose the seed(s). This coupling of seed and fruit development is generally not a

coincidence but a hormonally coordinated response: signals triggered by fertilisation drive both

processes together, which is why, in most flowering plants, seed formation and fruit formation

normally proceed hand in hand and a fruit typically forms only once its ovules have actually been

fertilised.

The wall of the mature fruit is called the pericarp, and it develops from the wall of the ovary. In

many species the pericarp differentiates further into three distinguishable layers: an outer

epicarp (often forming the fruit's skin or rind), a middle mesocarp (which may be fleshy, as in many

edible fruits, or fibrous, as described for coconut later in this chapter), and an inner endocarp

(which may be thin and membranous, or hard and stony, as in the familiar 'stone' of drupes such as

mango). The precise texture and thickness of each layer varies enormously across species and is

closely tied to how that particular fruit is dispersed.

A fruit that develops entirely, or almost entirely, from the ovary alone is called a true fruit --

mango and tomato are common examples, in which essentially all of the structure that eventually

becomes the fruit is traceable back to the ovary wall and the seeds within it. In some species,

however, one or more other parts of the flower -- most commonly the thalamus (receptacle), but

sometimes other accessory floral tissue -- contribute substantially to the structure that develops

alongside the ovary and that is eaten or dispersed as though it were simply 'the fruit'. Such

fruits, in which non-ovarian tissue makes up a significant, often the dominant, part of the mature

structure, are called false fruits. Apple is the standard textbook example: the fleshy, edible part

of an apple that is eaten develops mainly from the swollen thalamus surrounding the flower, while

the true fruit -- derived from the ovary itself -- is present only as the tough, papery core

containing the seeds, near the centre.

Fruit formation therefore represents the final structural transformation the flower undergoes as a

consequence of fertilisation: the whorls that once protected and attracted pollinators to the …