Hotbeds, to Make.—­Take dead leaves and stable-straw, with the dung, in the proportion of two double loads for a three-light frame.  Turn it over four or five times during a fortnight, watering it if it is dry.  Then mark out the bed, allowing 1 ft. or more each way than the size of the frame.  Shake the compost well up, and afterwards beat it down equally with the fork.  Place the frame on the bed, leaving the lights off for four or five days to allow the rank steam to escape.  Keep a thermometer in the frame, and as soon as the temperature falls below 70 degrees apply a lining of fresh dung to the front and one side of the bed, and when this again declines, add another lining to the back and other side, and so on from time to time as occasion requires.  The mats used for covering the frames in frosty weather should be made to fit the top, and not hang over the sides.

Houseleek.—­See “Sempervivum.”

Houstonia Coerulea.—­These hardy little evergreens are more generally known as Bluets.  They make charming ornaments for rock-work, planted between large stones, but in this position they need protection from severe frosts.  When planted in pots and placed in a cold frame they show to most advantage.  A mixture of leaf-mould and sand, and a moist but well-drained situation is what they delight in.  They bloom continuously from April to July.  Height, 3 in.

Hovea Celsi.—­A greenhouse shrub, which is evergreen and elegant when in flower in June.  A sandy loam and peat soil is most suitable, and it may be increased by cuttings planted in sand under a hand-glass.  Height, 3 ft.

Humea.—­A remarkably handsome and graceful plant, the leaves of which when slightly bruised yield a strong odour.  It is equally suitable for the centre of beds or large borders, and placed in pots on terraces or the lawn it is very effective.  The seed should be raised on a gentle hotbed, then potted off and kept in the greenhouse till the second year, when it may be turned out into a warm situation.  It generally succeeds better in such a position than in the greenhouse.  Flowers in July.  Height, 6 ft. to 8 ft.

Humulus Japonicus.—­(Japanese Hop).—­A hardy annual Hop of rapid growth, the leaves of which are splashed with white.  Useful for covering arbours, verandahs, etc.  A deep, loamy soil suits it best.  Increased by seed sown in gentle heat in February, and gradually hardened off.  Flowers in July.  Height, 20 ft.

Hutchinsia Alpina.—­This small alpine creeper is a profuse bloomer, its glistening white flowers being produced at all seasons.  It grows in moist vegetable mould, and bears transplanting at any season.  Care, however, is required to prevent its roots over-running and choking other things.  Height, 2 in.