The fruiting plant

The development of the true fruit involves either the expansion of the ovary into a juicy succulent structure, or the tissues becoming hard and dry. In false fruits other parts, such as the inflorescence, e.g. pineapple and mulberry, and the receptacle, as in apple, become part of the structure.

The succulent fruits are often eaten by animals, which help seed dispersal, and may also bring about chemical changes to break dormancy mechanisms. Some fruits (described as being dehiscent), release their seeds into the air. They do this either by an explosive method as seen in brooms and poppies; or by tiny feathery parachutes, seen in willow herb and groundsel. Dry fruits may rot away gradually to release their seeds by an indehiscent action. Different adaptations of fruit, many of which are of economic import ance, and the methods by which seeds are dispersed are summarized in Table 7.1 and illustrated in Figure 7.9.


Fruit set
The process of pollination, in most species, stimulates fruit set. The hormones, in particular gibberellins, carried in the pollen, trigger the production of auxin in the ovary, which causes the cells to develop. In species such as cucumber, the naturally high content of auxin enables fruit production without prior fertilization, i.e. parthenocarpy, a useful phenomenon when the object of the crop is the production of seedless fruit. Such activity can be simulated in other species, especially when poor conditions of light and temperature have caused poor fruit set in species such as tomato and peppers. Here, the flowers are sprayed with an auxin-like chemical, but the quality of fruit is usually inferior. Pears can be sprayed with a solution of gibberellic acid to replace the need for pollination. Fruit ripening occurs as a result of hormonal changes and involves in tomatoes a change in the sugar content, i.e. at the crucial stage called climacteric. After this point, fruit will continue to ripen and also respire after removal from the plant. Ethylene is released by ripening fruit, which contributes to deterioration in store. Early ripening can be brought about by a spray of a chemical, e.g. ethephon, which stimulates the release of ethylene by the plant, e.g. in the tomato.