Session 13 Reading
I FRUIT INTRODUCTION
Fruit, mature ovary in flowering plants, together with all inseparably connected parts of the flower. In strict botanical usage, the meaning may be restricted to the ovary alone. Commonly the term fruit is often restricted to succulent, edible fruits of woody plants, to melons, and to such small fruits as strawberries and blueberries. In nature, fruit is normally produced only after fertilization of ovules has taken place, but in many plants, largely cultivated varieties such as seedless citrus fruits, bananas, and cucumbers, fruit can matures without fertilization In either case, the maturation of the ovary results in the withering of stigmas and anthers and enlargement of the ovary or ovaries. Ovules within fertilized ovaries develop to produce seeds. In unfertilized varieties, seeds fail to develop, and the ovules remain their original size. The major service performed by fruit is the protection of developing seeds. In many plants, fruit also aids in seed distribution. See Seed.
II STRUCTURE OF FRUIT
As the ovary matures, its wall develops to form the pericarp, divided into three layers. The outermost, exocarp, is usually a single epidermal layer. The extent of the middle layer, mesocarp, and the inner layer, endocarp, varies widely, but in any single type of fruit one of the layers may be thick, the others thin. In fleshy fruits the pulpy layer is usually the mesocarp, as in peaches or grapes. The seed or seeds, which lie immediately within the pericarp, in some cases constitute the entire edible portion of the fruit. For example, the hard outer husk of a coconut is the complete pericarp, and the edible part inside, including the "milk," is the seed.
In typical cases, the fruit is confined to the ripened ovary, as in the pea pod; but in apples it includes ovary plus receptacle (other fused floral parts), in strawberries it is an aggregation of small individual fruits on a fleshy receptacle, called achenes, and in pineapples it is a development of an entire inflorescence, or cluster of flowers.
III TYPES OF FRUIT
Fruit is classified by several characteristics, the most significant being the number of ovaries included. A simple fruit is a single ovary, developed from the pistil of a single flower, which may be single or compound; an aggregate fruit is composed of many ovaries attached to a single receptacle; a multiple, or collective, fruit is formed from the coalesced ovaries of an entire inflorescence. Simple fruits are further subdivided into two categories, dry or fleshy. Ovary walls that develop into simple fruits are succulent when young, but as they mature, those of dry fruits lose most of their moisture, whereas those of fleshy fruits increase in size and moisture capacity. Dry fruits that dehisce, or split, when ripe are called dry dehiscent fruits; those that do not are indehiscent fruits.
IV FOOD VALUE
Fruits are eaten raw or cooked, dried, canned, or preserved. Carbohydrates, including starches and sugars, constitute the principal nutritional material. Citrus fruits, tomatoes, and strawberries are primary sources of vitamin C, and most fruits contain considerable quantities of vitamin A and vitamin B. Vitamin content is sharply reduced in storage and shipping of fresh fruits, but is maintained efficiently in frozen fruit. The jelly-making quality of many fruits is due to pectin, an important carbohydrate constituent. In general, fruits contain little protein or fat. Exceptions are avocados, nuts, and olives, which contain large quantities of fat, and grains and legumes, which contain considerable protein. Although the edible portions of fruits have a small ash content, fruits supply an important part of the mineral matter necessary in human diet. Dried or evaporated fruits contain much more nutritional material in proportion to their bulk than do fresh fruits, due to concentration by evaporation.
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