Many species of the genus Citrus (including sweet orange, tangerine, grapefruit, lemon, and lime) are grown for their edible fruits. Sweet oranges (Citrus sinensis) are the most widely grown fruit in the world, but in the nineteenth century they were considered luxuries and prescribed as cold remedies by physicians. Like other citrus fruits, the fruit of an orange is technically a hesperidium, a berry with a leathery rind and a juicy pulp that is formed of juice sacks borne on the inner layer of the fruit wall. The juice sacks fill the sections of the fruit and surround the seeds. The watery solution in the sacks is high in vitamin C. There are three main classes of oranges: Valencias, navels, and blood oranges. Valencias, with their deep orange color and rich flavor, are the source of most orange juice. Navel oranges, favored for eating, are the result of a mutation that produces a second ovary like structure (the navel) instead of seeds. Because they are seedless, navel oranges are all propagated by grafting. Blood oranges are seeded oranges named for the patches of deep red-purple color in the fruit.
Bananas became a major fruit crop in the twentieth century, prior to the use of refrigerated ships, bananas spoiled before they could reach markets outside the tropics. Wild bananas, native to eastern Asia, have seeds, but the common domesticated banana (Musa paradisiaca) is seedless and is the product of several cycles of hybridization followed by increases in chromosome number. Whether the fruit will be a tender and sweet yellow or red or a tough, starchy green plantain depends on the particular combination of chromosomes in the hybrid. Banana plants are giant herbs, not trees, and are propagated vegetatively by planting a piece of stem. Over the course of a year, the stem grows and produces a long terminal inflorescence of many clusters of female flowers along the flowering stalk and male flowers at the tip. The female flowers spontaneously mature, with each cluster forming a hand, or bunch, of bananas. An entire inflorescence can produce more than three hundred bananas, weighing 110 pounds. After fruiting, the shoot dies and is cut, allowing a sprout from the base to produce the next flowering stem.
Mangoes (Mangifera indica) are extremely common and important fruits in tropical areas, particularly in their native region of Southeast Asia, where the fruit pulp and even the seeds have been used for food. Mangoes are borne on trees that can grow only within tropical regions where there is adequate water in the summer. The fruit is a berry with musky yellow flesh surrounding a single large seed. Mangoes belong to the poison ivy family, some people are allergic to the latex produced in the skins. Mangoes were introduced into Brazil by the Portuguese in the early 1700's and subsequently spread to other areas of the New World tropics.
Melons, both common melons (Cucumis meld) and watermelons (Citrullus lanatus) belong to the same family (Cucurbitaceae) as squashes, but the latter are all native to the New World and the former to the Old World. All these species share the same kind of fruit, a pepo, which consists of a hard rind derived in part from the basal parts of the flower, and an edible fleshy layer of inner ovary tissue. Melons are monoecious vines with showy male and female flowers that require pollination to set fruit. Melons are native to Africa, where they were undoubtedly prized for their high water content and fresh flavor. Selection has led to numerous varieties, including cantaloupe, Crenshaw, honeydew, Persian, musk, and a variety of other melons that differ in the color and surface of the rind, color of the flesh, taste, and degree of sweetness.
Watermelons are native to sub-Saharan Africa, but they can be grown in temperate regions because they are annuals. The flesh is 87-92 percent water and is acidic enough to curdle milk. Recently, seedless types have been produced by artificially making triploid plants. The pollen of these triploids is sterile, and the seeds abort early. Farmers plant the triploids with fertile diploids. Pollen from the diploids fertilizes the ovules of the triploids and triggers fruit production. The seeds quickly die, but the fruit continues to mature into a seedless watermelon.
See also: Melanesian Islands, Polynesia
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