Fruit

B

Dry Fruits

Dry fruits are classified by whether they remain intact at maturity or open to release seeds. There are several types of intact, dry fruits. In samaras, the pericarp is light, relatively thin, and partly or completely fused to the seeds. It enlarges slightly, forming one or two small wings that aid in wind dispersal. Maples, ashes, and elms produce beautiful samaras that can be seen twirling slowly in gusts of wind. Nuts, on the other hand, have a relatively hard, heavy pericarp. Examples include chestnuts, hazelnuts, and acorns. In achenes, the seed is loosely attached to the pericarp, and the pericarp can be separated from the seed, as in sunflowers. Buckwheat and buttercups also produce achenes. A caryopsis, or grain, is a fruit in which the pericarp is tightly fused to the seed. A schizocarp is a twin fruit that separates into two one-seeded mericarps, types of fruit that often have tiny oil tubes in their walls. Examples include caraway and dill, whose fruits are harvested for their flavorful oils.

Dry fruits that open at maturity fall into several categories. Legumes, such as peas and beans, are one-chambered pods that split apart along two seams, exposing the seeds that lie within. Siliques and silicles split along two seams but contain two chambers. Siliques are more than three times longer than they are wide, while silicles are shorter. Broccoli, cabbage, and wallflower produce siliques, while dollar plants and alyssum produce silicles. A follicle, on the other hand, splits along one seam only. Milkweed, columbine, and larkspur produce follicles. Capsules split open in several ways, often along or between three or more seams, or between the top and bottom halves, as in primrose. Certain poppies produce capsules with rows of pores that release seeds when the capsule is shaken by the wind.

IV

Fruit and Seed Dispersal

Fruits enable seeds to be dispersed. Fruits are well adapted for dispersal by several mechanisms, including wind, water, and a variety of animals. The wings of maple and other samaras, for example, aid in wind dispersal. Some larger, heavier seeds are so rounded that the wind can roll them along, or they can roll down a hillside. Coconuts are carried great distances by ocean currents and germinate after they wash up on beaches. Sedge fruits have an inflated jacket and may float down a stream some distance from the parent plants.

Many types of animals play a role in the dispersal of fruits and seeds. Some fruits are covered with little hooks or sticky substances and catch in the fur or hide of animals such as coyotes, raccoons, and deer. As the animal moves about, the fruits or seeds are rubbed off by branches of shrubs or trees. Ducks may disperse fruits sticking in the mud on their feet. Woodpeckers often drop acorns while flying. Some birds eat fruits whose seeds stick to their beaks and then are rubbed off somewhere else. Seeds of other fruits pass intact through a bird's digestive tract. Ants remove the seeds from certain fruits before the fruits drop from the plant. They carry the seeds to their nests, remove and eat the appendages, and then deposit the seeds outside the nest.

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V

Nutritional and Commercial Importance

Many fruits taste sweet and delicious, and have the advantage of being relatively low in calories and high in nutrients. Grains and legumes are good protein sources, and other fruits contain many important vitamins and minerals as well as the complex carbohydrates needed for a balanced diet (see Human Nutrition). One medium-sized tomato, for example, has only 26 calories and provides vitamin C, vitamin B, beta carotene, calcium, phosphorus, iron, sodium, potassium, and zinc. Tomatoes and squash contain compounds called carotenoids and flavonoids, which are thought to provide protection from cancer. Fruits are also an excellent source of the fiber needed for a healthy digestive system.

Fruits are essential in the diet to prevent certain diseases. Scurvy, a potentially fatal disease marked by swollen joints, inflamed gums, and weakness, results from lack of vitamin C, the vitamin found in particularly high concentrations in oranges, lemons, and limes. Unprocessed grains and legumes, along with other foods, supply thiamine, or vitamin B₁, which prevents beriberi, a potentially fatal disease of the nervous system. Many fruits are also rich in vitamin A, which prevents night blindness, supports the immune system, helps bones grow, keeps skin healthy, and plays many other indispensable roles in maintaining health.

Fruits, including grains, occupy a central role in world agriculture. Adapted to a wide range of climates and soils, fruits are grown everywhere except the Arctic and the Antarctic. In the north and south temperate zones, the growing season typically extends from spring to autumn. Here, fields of corn, wheat, and oats dominate the farm landscape, along with orchards of plums, peaches, apples, and pears. Tomato, squash, eggplant, grapes, strawberries, and blueberries are also important crops in these regions. Leading producers of fruits grown in temperate regions include the United States, which produces over 229 million metric tons of corn and 894,000 metric tons of strawberries; China, with 20.4 million metric tons of apples and 25.5 million metric tons of tomatoes; and Italy, with 7.9 million metric tons of grapes.

In subtropical regions of the United States, China, Mexico, Argentina, India, Iran, and other countries, the mild year-round climate and longer growing season support rice, wheat, and millet, chili peppers, squash, oranges, lemons, avocados, figs, and olives. The most abundant harvests of these subtropical fruits include India’s 6.2 million metric tons of millet, Mexico’s 1.7 million metric tons of lemons and limes, and Brazil’s 19 million metric tons of oranges.

The tropics, however, with their abundant moisture and warm to hot temperatures, produce the most diverse and abundant fruits. Rice is a staple crop of many tropical countries, and plantations of banana and pineapple occupy millions of acres of land. Coconut, papaya, mango, star fruit, guava, macadamia, cashew, and melons are among the colorful fruits that flourish in this climate. In 2002 the leading producers of tropical fruits included India, with nearly 16.5 million metric tons of bananas; Thailand, with almost 2 million metric tons of pineapples; and Iran, with 875,000 metric tons of dates.

The cultivation of fruits, like all agricultural products, requires knowledge of the life cycle of the crop, the insects and diseases that plague it, and correct fertilization and irrigation practices. Fruit harvest is also important, particularly for fruits intended for fresh consumption. Fresh fruits often are transported long distances and must arrive at their destinations close to but not after the peak of ripeness, since ripe fruits decay rapidly.

Fruits are harvested by hand or, in areas where agriculture is industrialized, by machines. Fleshy fruits that will be eaten fresh typically are harvested by hand to ensure that they will be free from blemishes, a quality preferred by most consumers. Fleshy fruits that will be frozen, canned, dried, or made into jams or jellies are more commonly machine harvested.

Fleshy fruits that are not eaten fresh are stored under refrigeration and in a controlled atmosphere. Storage conditions differ depending on the type of fruit. Apples and some other fruits are stored in warehouses into which nitrogen gas is pumped; others are stored in warehouses with increased carbon dioxide and decreased oxygen. These storage conditions slow the physiological processes associated with ripening, and under these conditions, fleshy fruits can last several months (see Food Processing and Preservation). Grains are the exception, since unlike fleshy fruits, most can be harvested when ripe and stored for several years. They do need to be kept dry, but otherwise typically do not require special storage conditions.

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