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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.

Oenothera.—The Evening Primroses are most useful and beautiful plants, well suited for ornamenting borders, beds, edgings, or rock-work. All the species are free-flowering, and grow well in any good, rich soil. The annual and biennial kinds are sown in the open in spring. The perennials may be increased by dividing the roots, by cuttings, or by seed, the plants from which will flower the first season if sown early in spring. They bloom in June and July. Height, 6 in. to 4 ft.

Olearia.—These evergreen shrubs thrive in peat and loam, and may be increased by division of the roots. O. Haastii has foliage resembling the Box, and a profusion of white, sweet-scented flowers in summer: a chalk soil suits it admirably. Height, 3 ft. to 4 ft.

Omphalodes Verna.—A hardy perennial which may be grown under the shade of trees in ordinary soil. It produces its flowers in March, and is increased by dividing the roots in autumn. Height, 6 in.

Oncidium Sarcodes.—Plant these Orchids firmly in well-drained pots, using equal parts of live sphagnum and fibrous peat. Give one good watering as soon as the potting is finished, and stand them in a light, warm part of the greenhouse. They will require very little more water until the roots have taken hold of the soil—only sufficient to keep the pseudo-bulbs from shrivelling—and during the winter months scarcely any moisture is needed. They flower in August. Height, 1-1/2 ft.

Onions.—Require a deep, rich, heavy soil. Where the ground is not suitable it should have had a good dressing of rotten manure the previous autumn, and left in ridges during the winter. Level the ground, and make it very firm just before the time of sowing. The seed should be sown early in March for the main crop and for salad and pickling Onions, and in August for summer use. Thin out to about 6 in. apart, excepting those intended to be gathered while small. The Tripoli varieties attain a large size if transplanted in the spring. The Silver-skins do best on a poor soil. For exhibition Onions sow in boxes early in February in a greenhouse; when about 1 in. high prick out, 3 in. apart, into other boxes; give gentle heat and plenty of air, and when they have grown 6 in. high put them in a cool frame until the middle of April, when they must be planted in the open, 1 ft. apart.

Ononis Rotundifolia (Round-leaved Restharrow).—A charming hardy evergreen of a shrubby nature. It will grow in any ordinary garden soil, and is increased by seed, sown as soon as it is ripe. It is most effective in clumps, and blooms from June to September. Height, 1-1/2 ft.

Onopordon.—Half-hardy perennials of a rather interesting nature and of easy cultivation. Sow the seed any time between March and June. They require the protection of a frame or greenhouse during winter, and produce flowers in July. Height, 6 in. to 8 ft.

Onosma Taurica (Golden Drop).—This hardy herbaceous plant is very pretty when in flower, and suitable for rock-work. It requires a well-drained vegetable mould, and to be planted where it can obtain plenty of sun. It is increased from cuttings taken in summer, placed in a cucumber frame, kept shaded for about a fortnight, and hardened off before the winter. The flowers succeed one another from June to November. Height, 1 ft.

Opuntia Rafinesquii (Hardy Prickly Fig).—A dwarf hardy Cactus with sulphur-coloured flowers, produced from June to August; very suitable for dry spots in rock-work. It grows best in peat with a little sand, and is propagated by separating the branches at a joint, and allowing them to dry for a day or so before putting them into the soil. Height, 2 ft.

Orange, Mexican.—See "Choisya."

Orchids.—The four classes into which these charming and interesting plants are divided may be described as (1) those coming from the tropics, (2) from South Africa, (3) from the South of Europe, and (4) our native varieties. The first require a stove, the second a greenhouse, the third and fourth slight protection during winter. As their natural character differs so widely it is necessary to ascertain from what part of the globe they come, and to place them in houses having as near as possible the same temperature and humidity as that to which they are accustomed. The pots in which they are grown should be filled with fibrous peat and sphagnum moss, largely mixed with charcoal, and abundant drainage ensured. They are propagated by dividing the root stocks, by separating the pseudo-bulbs, and, in case of the Dendrobiums, by cuttings. Orchis Foliosa (Leafy Orchis) may be grown in the open ground in good sandy loam. When once established it is best not to disturb it, but if needed it may be increased by division, after the tops have died down. Orchis Fusca (Brown Orchis) may likewise be planted in the open, in a sheltered position, in fine loam and leaf-mould, the soil to be well drained, yet constantly moist.

Origanum Pulchellum.—Popularly known as the Beautiful Marjoram, this plant is useful for cutting for vases. It is perennial and hardy, and thrives in a dry situation with a sunny aspect and in a sandy soil. The bloom is in its best condition in October. The rooted shoots may be divided in spring or almost at any other period, or it may be propagated by taking cuttings in summer. Height, 1-1/2 ft.

Ornithogalum.—O. Arabicum bears a large white flower with a shiny black centre. It is a fine plant for pot culture, or it may be grown in water like the Hyacinth. It may be planted in the open early in spring in sandy loam and peat. Take it up before the frost sets in and store it in a dry place, as it requires no moisture while in a dormant state. In September the flowers are produced. Height, 6 in. O. Umbellatum (Star of Bethlehem) is a pretty little flower often found in English meadows, is quite hardy, and once established may be left undisturbed for years. It throws up large heads of starry flowers, which are produced in great abundance. While in a dormant state the bulbs should be kept almost dry. It is propagated by off-sets; flowers in May. Height, 1 ft.

Orobus.—These hardy perennials bear elegant Pea-shaped blossoms. The plants will grow readily in any light soil, and are easily increased by root-division in the spring, or by seeds. They flower in June. Height, 2 ft. to 3 ft.

Osmanthus.—These elegant hardy evergreen shrubs succeed best in light, sandy loam, and like a dry situation. They may be increased by cuttings of the young shoots with a little old wood attached, or they may be grafted on to common Privet. The variegated varieties are very beautiful. They grow well on chalk soils. Height, 4 ft. to 6 ft.

Othera Japonica.—A newly introduced evergreen shrub very similar to the Holly. It is perfectly hardy and may be treated in the same manner as that plant.

Ourisia Coccinea.—A hardy herbaceous, surface-creeping perennial of singular beauty as regards both leaf and flower. The soil in which it is grown must be well drained, a peat one being preferable; and the position it occupies must be well shaded from the rays of the midday sun. It flowers from May onwards to September, the cut bloom being admirable for mixing with fern leaves. As soon as new life starts in spring the roots may be divided. Height, 9 in.

Oxalis.—A genus of very pretty bulbous plants that thrive well in a mixture of loam, peat, and sand, or will grow in any light soil. Most of the tender kinds may be reared in a frame if protected from frost in the winter. After they have done flowering they should be kept dry until they begin to grow afresh. They are increased by off-sets from the bulb. The hardy species should be planted in a shady border, where they will grow and flower freely. The seeds of these may be sown in the open in spring. Some of the varieties have fibrous roots: these will bear dividing. They are equally suitable for pots, borders, or rock-work. Height, 9 in. to 3 ft.

Ox-Tongue.—See "Bugloss."

Oxythopis Campestris.—A hardy perennial with lemon-yellow flowers in June and July. It will grow in any good garden soil, and is propagated by seed only, which should be sown where the plants are intended to be grown. Height, 6 in.