Related to the lily, this underground bulb is prized around the world for the magic it makes in a multitude of dishes with its pungent flavor and odor. There are two main classifications of oniongreen onions (also called scallions) and dry onions, which are simply mature onions with a juicy flesh covered with dry, papery skin. Dry onions come in a wide range of sizes, shapes and flavors. Among those that are mild flavored are the white or yellow Bermuda onion, available March through June; the larger, more spherical Spanish onion, which is usually yellow skinned (but can be white) and typically in season from August to May; and the red or Italian onion, which is available year-round. The stronger-flavored globe onions can have yellow, red or white skins. They can range from 1 to 4 inches in diameter and in flavor from mildly pungent to quite sharp. Among the special onion varieties are three exceedingly juicy specimens. The Maui onion, hailingas its name impliesfrom the Hawaiian island of the same name, is sweet, mild and crisply moist. It can range in color from white to pale yellow and is usually shaped like a slightly flattened sphere. The Maui onion's season is from April to July. Vidalia onions are the namesake of Vidalia, Georgia, where they thrive. At their best, these large, pale yellow onions are exceedingly sweet and juicy. They're usually available much of the year in the regions where grown and from May through July elsewhere. The state of Washington is the source of Walla Walla onions, named after the city of the same name. Large, round and golden, they're in season from June to September but are often available outside their growing area only by mail order. Oso Sweet onions hail from South America and, as their name suggests, are extremely succulent and sweet and, in fact, contain almost 50 percent more sugar than Vidalias. They're available in specialty produce markets from January through March. Another import is the Rio Sweet onion, which is predictably sweet and available from October through December. Tiny pearl onions are mild-flavored and about the size of a small marble. They can be cooked (and are often creamed) and served as a side dish or pickled and used as a condiment or garnish (as in the Gibson cocktail). Boiling onions are about 1 inch in diameter and mildly flavored. They're cooked as a side dish, used in stews and pickled. When buying onions, choose those that are heavy for their size with dry, papery skins with no signs of spotting or moistness. Avoid onions with soft spots. Store in a cool, dry place with good air circulation for up to two months (depending on their condition when purchased). Humidity breeds spoilage in dry onions. Once cut, an onion should be tightly wrapped, refrigerated and used within four days. Most onions cause tearing (caused by sulfuric compounds) to some extentsome just watery eyes, others giant crocodile tears. Freezing the onion for 20 minutes before chopping helps, but then so does wearing safety goggles. Dried or freeze-dried onion by-products include onion powder (ground dehydrated onion), onion salt (onion powder and salt), onion flakes and onion flavoring cubes. Onions are also sold canned or pickled (usually pearl onions) and frozen (whole or chopped). Onions contain a fair amount of vitamin C with traces of other vitamins and minerals.