The annuals are increased by seeds; perennials by cuttings. =Polygala= (Milkwort). _Polygaleæ._ Seeds; sometimes by division, and by cuttings of young shoots under cover, particularly for tropical species. =Polygonatum= (Solomon's Seal). _Liliaceæ._ Propagated by seed and by divisions. =Polygonum= (Knot-Grass or Weed). _Polygonaceæ._ Seeds. The perennials are also increased by divisions of the root-stocks, and by cuttings. =Polypodium= (Polypody). _Filices._ Divisions usually. See Ferns. =Pomegranate= (_Punica granatum_). _Lythrœrieæ._ Largely by seeds, and all varieties are increased by cuttings, suckers, layers, and scarce sorts by grafting on a common sort. =Pomelo=, Shaddock (_Citrus Aurantium_, var. _pomelana_). _Rutaceæ._ Usually grown from seeds, but it may be budded upon pomelo or orange stocks, as in the Orange, which see. =Pontederia= (Pickerel Weed). _Pontederiaceæ._ Seeds rarely. Mostly by divisions. =Poppy.= See Papaver. =Populus= (Poplar, Aspen, Cotton-wood). _Salicineæ._ Seeds, sown as soon as ripe and raked in light soil. Suckers are also used. Most often increased by cuttings of ripe wood, taken in fall and spring. The weeping forms are stock-grafted upon upright sorts, as P. grandidentata. =Portugal Laurel.= See Prunus. =Portulaca= (Purslane, Rose Moss). _Portulaceæ._ The annuals are raised from seed. Varieties are sometimes propagated by cuttings. =Potato= (_Solanum tuberosum_). _Solanaceæ._ Tubers, either whole or variously divided. Also rarely stem cuttings. (See page 52.) =Potentilla=, including Horkelia, Sibbaldia (Cinquefoil, Five-Finger). _Rosaceæ._ Seeds, layers, divisions, green cuttings. =Poterium=, including Sanguisorba (Burnet). _Rosaceæ._ The herbaceous kinds are increased by seeds. The shrubs are raised from soft cuttings, under glass. =Premna=, Baldingera. _Verbenaceæ._ Seeds and soft cuttings. =Prickly Ash.= See Zanthoxylum. =Prickly Pear.= See Opuntia. =Pride of India.= See Melia. =Priestleya=, including Achyronia. _Leguminosæ._ Seeds. Cuttings of very young wood, under cover. =Prim.= See Ligustrum. =Primula=, Polyanthus (Primrose, Cowslip). _Primulaceæ._ Seeds, sown carefully in very fine soil, under glass. Some rare sorts are increased by division. =Prinos.= See Ilex. =Pritchardia.= _Palmæ._ Increased by seeds. =Privet.= See Ligustrum. =Prostanthera= (Australian Mint). _Labiatæ._ Seeds, divisions, and cuttings of growing shoots, usually by the last method. =Protea=, Erodendron. _Proteaceæ._ Seeds. Cuttings of growing wood, under cover. =Prune.= See Plum. =Prunus=, Amygdalus. _Rosaceæ._