Seeds, which must be stratified, or else sown as soon as ripe. They usually lie dormant the first year. Also by layers and cuttings of green-wood. Can be grafted upon other storaxes, or upon _Halesia tetraptera_. =Sugar Cane= (_Saccharum officinarum_). _Gramineæ._ Cuttings of the stems. The cuttings should possess a nope or joint which bears one or more good buds. These cuttings are planted directly in the field, and the plants will reach maturity in two or three months. Propagation by seeds has been supposed to be impossible, but recent experiments at Kew indicate that it can be done. =Sumach.= See Rhus. =Sundew.= See Drosera. =Sunflower.= See Helianthus. =Sun Rose.= See Helianthemum. =Swainsona.= _Leguminosæ._ Seeds. Green cuttings under cover. =Swan River Daisy.= See Brachycome. =Sweet Brier.= See Rosa. =Sweet Cicely.= See Myrrhis. =Sweet Pea.= See Lathyrus. =Sweet Potato= (_Convolvulus Batatas_). _Convolvulaceæ._ Sweet potato plants are grown in hot-beds, cold-frames or forcing-houses, from sound tubers of medium size. The tuber is laid upon a sandy or other loose bed, and is then covered with sand or sandy loam to a depth of one or two inches. Sometimes, to guard against rot, the tubers are not covered until the sprouts begin to appear. The tubers may be laid thickly upon the bed, but they are less apt to rot if they do not touch each other. Sometimes the tubers are cut in two lengthwise, the cut surface being placed down, in order to place all the plant-giving surface uppermost. In four or five weeks the young plants--three to five inches high--are pulled off and planted, and others soon arise to take their places. One hand should be held firmly upon the soil over the tuber, while the sprout is pulled off to keep it in place. Three or four crops of sprouts may be obtained from each tuber. =Sweet William= (_Dianthus barbatus_). _Caryophylleæ._ Seeds, sown in-doors or in the border. Division of the plants. Best results are obtained by starting new seedlings every other year. =Swertia.= _Gertianeæ._ Seeds, usually started in heat. =Sycamore.= See Platanus. =Symphoricarpus= (Waxberry, St. Peter's Wort, Snowberry-tree, Indian Currant). _Caprifoliaceæ._ Seeds, handled like those of blackberries. Also by suckers and cuttings. =Symphytum= (Comfrey). _Boragineæ._ May be increased by seeds and by division. Also by root-cuttings. =Symplocos=, including Hopea. _Styraceæ._ Seeds. Cuttings, in sand under glass. =Syngonium.= _Aroideæ._ Increased by dividing the stems into lengths of about three joints, and inserting them in pots in a brisk heat. The tops of plants may be cut off and inserted as large cuttings. =Syringa= (Lilac). _Oleaceæ._