Calendula (Marigolds).—­Very showy hardy annuals.  They merely require sowing in the open in autumn for an early display of bloom, or in spring for a later show, but the autumn sowing gives the more satisfaction.  Flower during June and July.  Height, 1 ft.

Californian Plants.—­Great care should be taken not to allow the sun to strike on the collar of any of the plants from California, as they readily succumb if it does so.

Calla.—­These showy plants, sometimes called Arum, are worth cultivating.  They make handsome pot-plants, bearing fine white flowers in the spring.  May be grown from seeds, or roots may be divided.  They are quickly increased by off-sets from the root in August or September.  Plant the off-sets from the fleshy roots singly in small, well-drained pots of sandy loam with one-fourth leaf-mould or well-rotted manure, and keep them in a very warm situation.  Water them well while in growth, scantily after the leaves begin to wither, and afterwards give only enough moisture to keep them alive.  Leave the plants in the light while the leaves die off, and then place them in a shed, in complete repose, for a month or so.  Re-pot them in October or November, and give plenty of water.  They may stand in saucers of water, but this must be changed daily.  They flower from May to July.  Height, 2 ft.

Callichroa.—­A hardy annual which well deserves a place in the garden border, both on account of its dwarf and slender habit and also the colour of its flowers.  It is satisfied with any ordinary soil.  The seed is raised on a hotbed in March, or in the open in April, and it blooms in the autumn.  Height, 1 ft.

Calliopsis.—­See “Coreopsis.”

Callirhoe (Digitata).—­Hardy annuals demanding but little attention. 
The seed is sown in the open in March.  Height, 1 ft.

Calochortus Luteus.—­This very handsome hardy perennial thrives best in sandy peat with a little loam.  It produces yellow flowers in July, and is propagated by offsets from the bulbs.  Height, 1 ft.

Caltha.—­Early-flowering, showy perennials, all thriving in a moist or boggy situation.  C. Leptosepala is especially choice, its pure white flowers resembling a water-lily.  They may be increased from seed, or by division.  Height, 1 ft.

Calthus Palustris Flore-Pleno (Double Marsh Marigold).—­This hardy herbaceous perennial is very useful for mixing with cut flowers.  It will grow anywhere, but prefers a clayey soil and a boggy situation, and may be increased by dividing the roots in spring.  A succession of flowers are borne from April to June.  Height, 9 in.

Calycanthus Floridus (Allspice).—­This shrub likes an open loamy soil; flowers in July, and is propagated by layers.  Height, 6 ft.

Calystegia.—­A perfectly hardy climbing convolvulus, and a beautiful plant for covering arbours, etc., growing 20 ft. to 30 ft. in one season.  It thrives in any loamy soil or situation; flowers from May to September, and may be increased by division of the roots.