The olive is grown in large quantities from seed, especially in Europe. The pulp is removed by maceration or by treating with potash. The pits should be cracked or else softened by soaking in strong lye, otherwise they will lie dormant for one or two years. Cuttings of any kind will grow. Limbs, either young or old, an inch or two inches in diameter, and from one to two feet long, are often stuck into the ground where the trees are to grow, or they are sometimes used in the nursery. Green cuttings, with the leaves on, are often used, being handled in frames or in boxes of sand. Chips from old trunks, if kept warm and moist, will grow. The olive is often propagated by truncheons of trunks. A trunk two or three inches in diameter is cut into foot or two foot lengths, and each length is split through the middle. Each half is planted horizontally, bark up, four or five inches deep, in warm moist soil. The sprouts which arise may be allowed to grow, or they may be made into green cuttings. Knaurs (see page 56) are sometimes used. The olive can be budded or grafted in a variety of ways. Twig-budding and plate or flute-budding give admirable results. Twig-budding is the insertion of a small growing twig which is cut from the branch in just the manner in which shield-buds are cut. =Omphalodes=, Picotia. _Boragineæ._ Freely increased by means of seeds planted in spring, or by divisions. =Oncidium.= _Orchideæ._ Division. In some species detachable buds are produced in the inflorescence, and these give young plants. (See also under Orchids.) =Oncosperma=, Keppleria. _Palmæ._ Propagated by seeds or by suckers. =Onion= (_Allium Cepa_). _Liliaceæ._ Onions are mostly grown from seeds, which must be sown as early as possible in spring; or in the south they may be sown in the fall. They are also grown from "tops," which are bulblets borne in the flower cluster. These are planted in the spring, or in the fall in mild climates, and they soon grow into large bulbs. "Sets" are also used. These are very small onions, and when planted they simply complete their growth into large bulbs. Sets are procured by sowing seeds very thickly in poor soil. The bulbs soon crowd each other, and growth is checked, causing them to ripen prematurely. Good sets should not be more than a half inch in diameter. Very small onions which are selected from the general crop--called "rare-ripes"--are sometimes used as sets, but they are usually too large to give good results. Some onions--the "multiplier" or "potato onions"--increase themselves by division of the bulb. The small bulb, which is planted in the spring, splits up into several distinct portions, each one of which will multiply itself in the same manner when planted the following year. =Onobrychis= (Saintfoin). _Leguminosæ._