Neuvusia Alabamensis.—­A tamarix-like shrub, bearing clusters of white flowers early in spring.  Will grow in any soil or situation.  Increased by cuttings placed in sand under glass.

Nicotiana (Tobacco Plants).—­Very showy half-hardy annuals.  N. Affinis bears long, tubular, sweet-scented, white flowers in July, and grows to the height of 3 ft.  N. Virginica produces immense leaves and pink flowers, and the plants are 4 to 5 ft. high.  The seed is sown on a hotbed in spring, and when the second or third leaf appears the plants are put into small pots and placed in a frame till the end of May, when they are transferred to the border.

Nierembergia (Cup Flowers).—­These elegant half-hardy annuals grow well in any light soil, but prefer a mixture of sandy loam and leaf-mould.  Sow the seed in March or April in slight heat, harden off, and plant out in May as soon as all fear of frost is over.  They flower in July.  Height, 9 in. to 1 ft.

Nierembergia Rivularis.—­This herbaceous plant is of a creeping nature; it has deep green ovate foliage and large saucer-shaped white flowers.  It needs a moist position, and is increased by division.  The bloom is produced throughout June, July, and August.  Height, 3 in.

Nigella.—­These hardy annuals, a species of Fennel-flower, are both curious and ornamental.  Perhaps the best known among them is N. Hispanica, or Love-in-a-Mist.  They only require sowing in the open in spring—­but not before the middle of March—­to produce flowers in July and August.  Height, 9 in. to 2 ft.

Night-scented Stocks.—­See “Mathiola.”

Nolana.—­Hardy annuals that are suitable for the border, as they are very showy when in flower.  The seed should be sown in spring on a gentle hotbed, and the plants transferred to the garden about the middle of May.  N. Atriplicifolia may be sown in the open in the autumn.  They flower in July and August.  Height, 6 in. to 2 ft.

North Borders, Plants suitable for.—­Hardy Camellias, Chrysanthemums, black and green Tea Plant, Rhododendrons, Ferns, Red Currants, Morello Cherries, and spring and summer cuttings of all sorts.

Nuttallia.—­This early-flowering shrub is only hardy in the south and south-west of our country.  It requires a light, rich soil, and may be increased by division.  Racemes of white flowers are produced during February and March.  Height, 2 ft.

Nycterina.—­Exquisite little half-hardy plants, suitable for pots or rock-work.  The seed should be sown early in spring on a gentle hotbed, and the young plants transferred to the pots or open ground at the end of May, using a light, rich soil.  Height, 3 in.

Nymphaea Alba.—­A hardy aquatic perennial, frequently found in our ponds.  It flowers in June, and may be increased by dividing the roots.  Height, 1 ft.

O

Odontoglossum Grande.—­A most beautiful orchid, delighting in a temperature of from 60 to 70 degrees and an abundance of water during summer, but good drainage is essential.  The blooms are yellow, spotted and streaked with venetian red, and are often 6 in. across.  The pots should be two-thirds filled with crocks, then filled up with fibrous peat and sphagnum moss.  During winter only a very little moisture should be given.