Cypripedium.—Beautiful terrestrial orchids, requiring to be planted in peat soil, in a cool and rather shady situation. C. spectabile, 1½ to 2 ft., white and rose colour, in June, is a lovely species, as is C. Calceolus, 1 ft., yellow and brown, in May; all are full of interest and beauty.
Delphinium.—The Larkspur family, tall showy plants, with spikes of blue flowers in July. Distinct sorts are D. grandiflorum and D. grandiflorum flore-pleno, 2 to 3 ft., of the richest dazzling blue, flowering on till September; D. chinense, 2 ft., blue, and its double-flowered variety, are good, as is D. Barlowi, 3 ft., a brilliant double blue-purple. D. nudicaule, 2 ft., orange-scarlet, very showy, is best treated as a biennial, its brilliant flowers being produced freely in the second year from the seed.
Dianthus.—Chiefly rock plants with handsome and fragrant flowers, the smaller sorts growing in light sandy soil, and the larger border plants in rich garden earth. Of the dwarfer sorts for rock gardens, D. alpinus, D. caesius, D. deltoides, D. dentosus, D. neglectus, D. petraeus, and D. glacialis are good examples; while for borders or larger rockwork D. plumarius, D. superbus, D. Fischeri, D. cruentus, and the clove section of D. Caryophyllus are most desirable.
Dicentra.—Very elegant plants, of easy growth in good soil. D. spectabilis, 2 to 3 ft., has paeony-like foliage, and gracefully drooping spikes of heart-shaped pink flowers, about May, but it should have a sheltered place, as it suffers from spring frosts and winds; D. formosa and D. eximia, 1 ft., are also pretty rosy-flowered species.
Dictamnus.—D. Fraxinella is a very characteristic and attractive plant, 2 to 3 ft., with bold pinnate leaves, and tall racemes of irregular-shaped purple or white flowers. It is everywhere glandular, and strongly scented.
Digitalis.—Stately erect-growing plants, with long racemes of pouch-shaped drooping flowers. The native D. purpurea, or foxglove, 3 to 5 ft., with its dense racemes of purple flowers, spotted inside, is very showy, but is surpassed by the garden varieties that have been raised. It is really a biennial, but grows itself so freely as to become perennial in the garden. An erect flowered form is called gloxinioides. The yellow-flowered D. lutea and D. grandiflora are less showy. Good garden soil, and frequent renewal from seeds.
Doronicum.—Showy composites of free growth in ordinary soil. D. caucasicum and D. austriacum, 1 to 1½ ft., both yellow-flowered, bloom in spring and early summer. D. plantagineum excelsum, 3 to 5 ft. high, is the best garden plant.
Draba.—Good rockwork cruciferous plants. D. alpina, D. aizoides, D. ciliaris, D. Aizoon, and D. cuspidata bear yellow flowers in early spring; D. cinerea and D. ciliata have white flowers. Gritty well-drained soil.
Dracocephalum.—Handsome labiate plants, requiring a warm and well-drained soil. D. argunense, 1½ ft., D. austriacum, 1 ft., D. grandiflorum, 1 ft., and D. Ruyschianum, 1½ ft., with its var. japonicum, all produce showy blue flowers during the summer months.
Echinacea.—Stout growing showy composites for late summer and autumn flowering, requiring rich deep soil, and not to be often disturbed. E. angustifolia, 3 to 4 ft., light purplish-rose, and E. intermedia, 3 to 4 ft., reddish-purple, are desirable kinds. E. purpurea (often called Rudbeckia) is the showiest species. Height 3 to 4 ft., with rosy-purple flowers.