Fruit Structure and Function

One characteristic that distinguishes flowering plants from other seed plants is that ovules are enclosed in an ovary. Fertilization of the egg in a flowering plant stimulates growth in both ovule and ovary. Growth and maturity of the ovary result in a fruit. Most ovaries are small at  fertilization, often less than 2 mm. Fruits vary greatly in size, however; beans, apples, and watermelons all have ovaries of similar size in the flower stage, but very different-sized mature fruits. As an ovary develops into a fruit, its wall, the pericarp (Gr: peri = around), thickens and often differentiates into distinct layers, the exocarp (exo = outside, carpus = fruit), mesocarp (meso = middle), and endocarp (endo = inside), or sometimes only into exocarp and endocarp. These layers are generally more conspicuous in fleshy fruits than in dry ones.

As the fruit develops, it protects the developing seeds and the embryos they in turn contain. The mature fruit may be adapted to protect the seeds until they are mature, or it may be adapted to disperse them. Mechanisms of dispersal are varied and sometimes quite surprising. Among the more curious are those with exploding fruits such as the "touch-me-not", Impatiens, which derives its name from having impatient fruit which explode on contact. Other mechanisms are more obvious such as the light tufts of hairs for wind dispersal or the stiff hooks for animal dispersal.