Clianthus.—­A genus of very elegant, free-flowering, evergreen greenhouse shrubs.  They flourish in the border of the conservatory (or against a south wall if protected from cold) in an equal mixture of loam, peat, and sand.  Cuttings root freely in the same soil under glass.  Seed sown early in spring produce flowers the first year, in May.  Height, 3 ft. to 4 ft.

Clintonia.—­Very pretty half-hardy annuals; useful for beds, edging, pots, or rock-work.  They produce an abundance of Lobelia-like flowers in August.  Sow the seed in the open in spring.  Height, 6 in.

Clitoria.—­A greenhouse climbing or trailing plant, which thrives in a mixture of loam, peat, and sand.  Cuttings will strike in heat, but it is more readily grown from seed.

Clivias (Caffre Lilies).—­Most beautiful evergreen plants for the greenhouse.  The soil most suitable for them is a compost of leaf-mould, loam, and sand.  Give a liberal supply of water when in full growth, but from September to February keep them only moderately moist.  Shade from strong sunshine, and keep the temperature at from 60 to 70 degrees.  They will not bear much disturbance.  Seed may be sown in bottom-heat early in spring, or they may be increased by suckers.

Cobaea Scandens.—­This rapid climber is well adapted for the conservatory, but it will thrive in the open air if the root is protected during the winter.  If planted against a rough wall its tendrils will catch in the crevices and support it without any assistance.  It requires plenty of room and a rather poor soil, otherwise it runs to leaf instead of to bloom.  The tops of the shoots should be constantly pinched off, to induce thickness of growth.  Cuttings of firm side-shoots taken in summer will root under glass in a little moist heat; but it is best raised from seed, sown sideways, in a hotbed in March.  Its blue and purple flowers are produced in August.  Height, 10 ft. to 20 ft.

Cob Nuts.—­See “Filberts.”

Cockscomb.—­These tender annuals should be sown on a moderate hotbed in March or April, in pans of leaf-mould and sand, covering with 1/4 in. of soil.  When a couple of inches high place them in small pots, replace them on the hotbed, and give shade till they have taken fresh root.  When the weather is favourable let them have a moderate amount of fresh air.  Afterwards shift them into larger pots, and when the combs are full grown place them in the greenhouse, taking care not to allow any damp to lodge on them, at the same time supplying them well with water and all the air possible.  Height, 9 in. (See also “Celosia.”)

Codonopsis.—­These hardy perennials are best grown in sandy peat and loam.  They are easily raised from seed or cuttings, and produce their flowers in July and August.  Height, 1 ft.

Coix Lachryma (Job’s Tears).—­A half-hardy, annual, ornamental grass bearing clusters of beautiful pearl-like seeds.  Sow in a warm spot in April, barely covering the seed with fine soil, and keep the surface of the ground moist till germination is ensured.  Height, 1-1/2 ft.