Nepeta.—N. Mussinii, 1 ft., is a compactly spreading greyish-leaved labiate, with lavender-blue flowers, and is sometimes used for bedding or for marginal lines in large compound beds.
Nierembergia.—N. rivularis, 4 in., from La Plata, has slender, creeping, rooting stems, bearing stalked ovate leaves, and large funnel-shaped white flowers, with a remarkably long slender tube; especially adapted for rockwork, requiring moist sandy loam.
Nymphaea.—See [Water-Lily].
Oenothera.—The genus of the Evening Primrose, consisting of showy species, all of which grow and blossom freely in rich deep soils. Oe. missouriensis (macrocarpa), 6 to 12 in., has stout trailing branches, lance-shaped leaves and large yellow blossoms; Oe. taraxacifolia, 6 to 12 in., has a stout crown from which the trailing branches spring out, and these bear very large white flowers, changing to delicate rose; this perishes in cold soils, and should therefore be raised from seed annually. Of erect habit are Oe. speciosa, 1 to 2 ft., with large white flowers; Oe. fruticosa, 2 to 3 ft., with abundant yellow flowers; and Oe. serotina, 2 ft., also bright yellow.
Omphalodes.—Elegant dwarf boraginaceous plants. O. verna, 4 to 6 in., a creeping, shade-loving plant, has bright blue flowers in the very early spring; O. Luciliae, 6 in., has much larger lilac-blue flowers, and is an exquisite rock plant for warm, sheltered spots. Light sandy soil.
Onosma.—O. taurica, 6 to 8 in., is a charming boraginaceous plant from the Caucasus, producing hispid leaves and cymose heads of drooping, tubular, yellow flowers. It is of evergreen habit, and requires a warm position on the rockwork and well-drained sandy soil; or a duplicate should be sheltered during winter in a cold, dry frame.
Ornithogalum.—The Star of Bethlehem. O. arabicum can only be grown in the warmest parts of the kingdom, and then requires protection in winter. Other species, all bulbous, are O. nutans, O. pyramidale, O. pyrenaicum, and the common Star of Bethlehem, O. umbellatum; all are easily grown, and have white flowers.
Ostrowskya magnifica.—A magnificent bellflower from Bokhara, 4 to 5 ft. high, and white flowers tinted and veined with lilac, 3 to 5 in. across. Requires rich, gritty loam of good depth, as it produces tuberous roots 1 to 2 ft. long.
Ourisia.—Handsome scrophulariaceous plants, from Chile, thriving in moist, well-drained peaty soil, and in moderate shade. O. coccinea, 1 ft., has erect racemes of pendent crimson flowers.
Papaver.—The Poppy. Very showy plants, often of strong growth, and of easy culture in ordinary garden soil. P. orientale, 3 ft., has crimson-scarlet flowers, 6 in. across, and the variety bracteatum closely resembles it, but has leafy bracts just beneath the blossom. P. alpinum, 6 in., white with yellow centre; P. nudicaule, 1 ft., yellow, scented, and P. pilosum, 1 to 2 ft., deep orange, are ornamental smaller kinds.