Seeds, which are rolled up in a ball of clay and dropped into a pond, or sown in pots which are then submerged in shallow water, either in-doors or out. Usually increased by portions of the root-stocks, which are sunk in the pond and held by stones, or the tender species placed inside, in pans of water. Some species produce tubers on the root-stocks, which are used for propagation. =Nyssa= (Pepperidge, Sour Gum, Tupelo-tree). _Cornaceæ._ Increased by seeds and by layers. The seeds should be sown as soon as ripe or else stratified. They usually lie dormant the first year. =Oak.= See Quercus. =Obeliscaria.= See Rudbeckia. =Ochna.= _Ochnaceæ._ During summer, cuttings may be made of growing shoots. =Odontoglossum.= _Orchideæ._ Division. (See also under Orchids.) =Œnocarpus.= _Palmæ._ Propagated by seeds or by suckers. =Œnothera=, including Godetia (Evening Primrose). _Onagrameæ._ Seeds may be sown in spring or summer. Divisions may be made. Cuttings of perennials should be placed in a cool frame in the early part of the season before flowering begins. =Okra=, Gumbo (_Hibiscus esculentus_). _Malvaceæ._ Seeds, sown where the plants are to stand, or started in pots often in the north. =Olax.= _Olacineæ._ Grown from cuttings of firm or mature shoots in heat. =Olea.= _Oleaceæ._ The ornamental species are grown from cuttings of ripened shoots, either under frames or in the border, and also by seeds. For propagation of _O. Europæa_, see Olive. =Oleander.= See Nerium. =Olearia=, Eurybia. _Compositæ._ Seeds. Readily increased by cuttings of growing shoots placed in a frame. =Oleaster.= See Elæagnus. =Olive= (_Olea Europæa_). _Oleaceæ._