DAHLIA, a genus of perennial herbs of the family Asterace,r, closely related to the genera Bidens, Coreopsis and Cosmos (q.v.), which are distinguished by technical characters. In deed, Cosmos diversifolius, or black cosmos, is well known to American gardeners as Bidens and Dahlia. The true dahlias are much con fused as to nomenclature, only about 10 well authenticated species being recognized out of a large number of synonyms. With few ex ceptions (Central American species) they are natives of Mexico. Six species are cultivated, but only two of these (D. rosea and D. juaresii) are of wide horticultural importance. The former has given rise to several thousand hor ticultural varieties since 1814, when well-marked double varieties first appeared; the latter, which was introduced about 1879, has produced a con siderable _number popularly known as cactus dahlias. There are also many single varieties. Considering the short time the dahlias have been in cultivation (since 1879) they have attained a very high rank as a garden plant, being num bered among a dozen plants to have special societies and exhibitions, both in Europe and America. Besides the cactus forms, which are
less formal than the earlier double varieties, there are many forms and sizes ranging in color from white to yellow and deep red, but deficient in the shades of blue. The plants may be propagated by seeds for obtaining new va rieties, by division of the underground parts, or commercially by cuttings. They succeed well in almost any good soil, the tubers or the young plants being set in beds as soon as danger from frost is past. When frost has killed the tops in the autumn the plants are dug and the tubers stored in a cool, dry cellar until spring, or until they are needed for obtaining cuttings, when they are placed on greenhouse benches and forced. Few pests attack the plants. Consult Peacock, 'The Dahlia,' and other literature mentioned in article "Dahlia* by Bailey in 'Cyclopedia of American (Dah lia, a Talk About,' Cornell University Experi ment Station Bulk& 128.