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