Readily increased by seeds or divisions. =Herbertia.= _Irideæ._ Propagated by means of seeds or bulbels. =Herb-Robert.= See Geranium. =Hesperis= (Dame's Violet, Rocket). _Cruciferæ._ The single sorts are increased by seeds; the double forms by carefully dividing the roots, or by cuttings. =Heterocentron.= _Melastomaceæ._ Propagated by cuttings. =Heuchera= (Alum Root). _Saxifrageæ._ Seeds. Readily increased by dividing the crowns during spring. =Hevea=, Micrandra, Siphonia. _Euphorbiaceæ._ Cuttings should be made of half-ripened wood, and inserted in sand under glass. =Hibbertia=, including Cyclandra, Pleurandra. _Dilleniaceæ._ Cuttings, in sandy peat under glass. =Hibiscus.= _Malvaceæ._ Seeds sometimes. Also by divisions and layers. Cuttings of green-wood are commonly used, made in summer for hardy species or in early spring for tender ones. Cuttings of ripened wood may be taken in fall, and stored until spring in a rather dry place. The variegated sorts do better if grafted upon strong stocks. =Hicoria=, Carya (Hickory, Pecan, etc.). _Juglandeæ._ Increased chiefly by seeds, which should be stratified; also by root-sprouts. Seeds are sometimes planted at intervals in the field where the trees are to stand; but this practice is not to be recommended. The hickory can be grafted. Best results are obtained by veneer or splice-grafting in winter, on potted stocks. Cleft-grafting can be employed out-doors. Saddle-grafting upon young twigs is sometimes used. See also Pecan. =Hippeastrum= (Equestrian Star). _Amaryllideæ._ Seeds may be sown as soon as ripe in well-drained pots or pans of sandy loam, slightly covered, and placed in a temperature of about 65°. For increasing by divisions--which is the usual way--the old bulbs should be taken from the pots and carefully separated, with the least possible injury to the roots. This should be done when the plants are at rest, and the offsets should be placed singly in pots. Keep the bulb about two-thirds above the level of the soil, dispose the roots evenly, and plunge in bottom heat, in a position exposed to the light. =Hippomane=, Mancinella. _Euphorbiaceæ._ Propagated by cuttings, placed in sand under glass. =Hippophaë= (Sallow Thorn, Sea Buckthorn). _Elæagnaceæ._ May be increased by seeds, suckers, layers, and cuttings of the roots. =Hoffmannia=, Higginsia. _Rubiaceæ._ Insert cuttings in sandy soil under cover, in bottom heat. =Hog Plum.= See Spondias. =Holbœllia.= _Berberideæ._ In spring, cuttings may be made of half-ripened shoots. =Holly.= See Ilex. =Hollyhock= (Althæa). _Malvaceæ._