Cornel.—­See “Cornus.”

Cornflower.—­See “Cyanus.”

Corn Salad (Lamb’s Lettuce).—­Sow in drills—­the plants to stand 6 in. apart—­from March till August, in well-drained sandy loam.  Autumn sowings will stand the winter and prove useful in early spring.  It must be gathered young.

Cornus Canadensis (Canadian Cornel).—­A pretty herbaceous plant, suitable for moist parts of rock-work.  It is very hardy, likes a light soil, and produces flowers from June to August.  The roots may be divided in autumn, or in the early part of spring.  Height, 8 in.

Cornus Mas (Cornelian Cherry).—­This hardy deciduous shrub does well in common soil if a fair amount of moisture be given.  Its yellow flowers are produced on bare stems from February to April.  It may be increased by seeds, cuttings, or layers, autumn being the time to propagate.

Coronilla.—­The greenhouse shrubs should be grown in peat and loam.  They are raised by seeds and by cuttings.  Most of the hardy perennials need protection in winter, therefore they are best grown in pots.  These are propagated by seed or division.  The annuals need no special treatment.

Coronilla Iberica.—­A pretty creeping hardy perennial suitable for rock-work, on which its bright yellow flowers are very attractive during June and July.  It thrives best in a mixture of peat and loam, and may be increased by seeds or division of the roots.  Height, 6 in.

Correa Cardinalis.—­An evergreen greenhouse shrub.  Place in equal parts of sand and loam, and propagate by cuttings, which should have plenty of room, as they are liable to damp off.  July is its flowering season.  Height, 4 ft.  C. Magnifica is also a capital plant.

Cortusa Matthioli.—­This ornamental hardy herbaceous plant thrives best in a mixture of peat and loam.  It is advisable to give protection to the roots in winter.  It may be increased by seeds or by division of the roots.  It makes a good pot-plant, and produces flowers in May and June.  Height, 1 ft.

Corydalis (Fumitory).—­These low-growing perennials are suitable for dry positions on rock-work.  They are not particular as to soil, and may be increased by division of roots, while some scatter seed in abundance.  Their flowering period extends over many months.  Height, 6 in. to 1 ft.

Cosmea Bipinnata.—­A very pretty half-hardy annual which flowers in July.  Sow the seed early in spring on a slight hotbed covered with glass, and transplant to the flower border at the end of May.  Height, 2 ft.

Cosmos.—­Pretty plants, the flowers resembling a single Dahlia.  They are mostly hardy, but some need protection.  The annuals should be raised on a hotbed in February and be planted out in May.  The perennials, too, are brought forward in heat.  Some flower in June, others in September.  Height, 1 ft. to 3 ft.

Cotoneaster.—­Evergreen shrubs which will grow in any soil and are easily increased by layers.  C. Hookeriana attains the dimensions of small trees, and produces a profusion of white flowers and bright crimson berries.  C. Simonsii is largely used as a hedge.  Height, 6 ft. to 8 ft.  C. Rupestris is a small-leaved, prostrate perennial species, bearing white flowers from May to August, followed by red berries.  Height, 3 in.