The number of edible tropical fruits is legion. Thousands of them are used daily by the native peoples, and most of these are unknown to the white man. There are 250 edible fruits in the Philippine Islands alone. Sooner or later the people of the United States as well as of other temperate regions will have to turn to a greater extent to the tropics to supplement their own food resources, and fruits are among the best products that the tropics have to offer. Improved methods of transportation will make it possible to use fruits actually grown in the tropics, while Florida and California have a climate favorable to the cultivation of many tropical species. Several tropical fruits have already been exploited. The banana and pineapple are now as familiar as the apple and pear, and citrus fruits are known the world over. In comparison with the fruits of temperate regions, tropical fruits have been much neglected horticulturally and few improvements have been made over the wild product. This condition is now being remedied and with the use of scientific methods of fruit growing the products of the tropics should be all the more valuable. While edible fruits occur in a vast number of families, they are particularly important in the Anacardiaccae, Annonaceac, Myrtaceae, Rutaceae, Sapotaceae, and Sapindaceae. Of these the Rutaceae is the best known and most important, for it is the source of the citrus fruits.
The citrus fruits were domesticated from wild ancestors in Eastern and Southern Asia in very early time. Some of them have been cultivated for over 3000 years. They were sometimes grown for other purposes than eating. Citron, for example, was planted in the famous Hanging Gardens of Babylon for use in toilet water and pomades. These fruits were early introduced into the Mediterranean region, where they have always been an important crop. As many as 100 species of Citrus have been described, many of which are probably of hybrid origin. Only a few, however, are of commercial importance.
The citrus fruits are thorny aromatic shrubs or small trees. The leathery evergreen leaves are glandular dotted and, although they appear to be simple, are actually unifoliate-compound leaves with a joint between the leaf blade and stalk. The white or purplish flowers are solitary, but produced in great profusion, and often very fragrant. The