[Illustration: A List of the most Popular American Onions.] An onion set is merely an immature bulb. Sets vary from the size of a large pea up to that of a walnut. When the seed is sown thickly the bulbs have no chance to grow, and the summer weather quickly ripens the tops, completely suspending the growth of the bulb. In some parts of the country onion sets cannot be grown with profit, as the tops refuse to die and the bulbs or sets do not ripen properly. In nearly all parts of the United States onions can be grown direct from the seed the first year; especially from seed grown around Philadelphia, which is earlier than Western-grown. It is quite customary in the South to sow onion seed in late summer or autumn; in August or September. This will give early spring onions of marketable size. In the North, within quite recent years, it has become the practice to sow onion seed in frames, in fall or early spring, and transplant the young onions to the open ground. This is sometimes spoken of as the new onion culture. Onion sets or young plants should be placed 3 or 4 inches apart, in rows a foot apart, if to be cultivated by hand; the rows farther apart if for horse work. The onion is hardy. Many varieties will live in the open ground over winter, if covered (at the North) with light litter. It is in this way that shoots for bunching are obtained early in the spring. The seed should be sown for sets when the apple is in bloom. Sets may be put into the ground earlier; in fact, as soon as the ground can be worked. The set should not produce seed the first year, though it often does so. It should, on the contrary, grow to the size of say 3 inches, and then ripen for winter storage. Excessively large onions are not desirable. To hasten maturity, the tops may be broken down or the roots may be cut by running a knife or sharp plow or cultivator along one side of the row. The onion, under favorable circumstances, will produce a crop of 800 bushels (fifty-six pounds to the bushel) per acre; though 500 bushels is nearer the average product. [Illustration: Weeding a Field of Onion Sets on our Bucks County Seed Farm near Philadelphia.] =Storage.=--The storage of onions and onion sets is simple. The bulbs should first be ripened on the ground, by a brief exposure to wind and sun. This completes the wilting of the tops. They should then be spread out on ventilated trays or racks, or a few inches in depth on a floor, in a dry, shady place, where the air is good, preferably a loft; not a damp cellar. Freezing will not injure them, but they must not be handled when they begin to thaw, or they will rot. They must not be bruised during the operation of gathering or during the process of storage.