DAHLIA, a genus of herbaceous plants of the natural order Composites, so called after Dr Dahl, a pupil of Lin naeus. The dahlia is indigenous to Mexico, where it flourishes in sandy tracts at a height of 5000 feet above sea-level. Two cultivated species are distinguished by some botanists, D.frustranea and D. superflua, the outer involucre in the former being spreading, in the latter reflexed. The flowers have a chaffy receptacle, a double involucre, and no pappus. The roots or tubers are spindle-shaped, and grow in bundles; they were at one time used as food in France; but their acrid flavour occasioned their rejection as an esculent. They may be stored in winter in the same manner as potatoes. The flowers, at the time of the first introduction of the plant, were single, with a yellow disc and dull scarlet rays; under cultivation, since 1802 in France and 1804 in England, flowers of numerous brilliant hues, with the elements of the disc converted into rayflorets, have been produced. The flower has been modified also from a flat to a globular shape, and the arrangement of the florets has been rendered quite distinct in the ranunculus and anemone-like kinds. The ordinary natural height of the dahlia is about 7 or 8 feet, but one of the dwarf races grows to only 18 inches. With changes in the flower, changes in the shape of the seed have been brought about by cultivation; varieties of the plant have been produced which require more moisture than others; and the period of flowering has been made considerably earlier. In 1808 dahlias were described as flowering from September to November, but some of the dwarf varieties at present grown are in full blossom in the middle of June. The nature of the season has a marked effect upon certain kinds of dahlia, so that those which ...