Properties and uses
Onions are a staple of every cuisine the world over, valued as a lubricant as well as flavouring, and for the fact that they can be plaited and stored for use throughout winter and spring.  Like garlic, shallots and spring onions, they are derived from an unidentified (probably central Asian) wild species.  All onions consist of a bulb that grows underground with green shoots above, the bulb having a papery outer skin covering layers of crisp, pale flesh.  Numerous varieties have been cultivated to meet different culinary demands: hardy, over-wintering main crop varieties are planted in August, those requiring a shorter growing season are planted in spring; there are salad onions, tiny pickling onions and a host of cooking onions: Spanish onions are the largest, with brown skins and a sweetish mild taste; yellow onions are hot and pungent; red-skinned onions are sharper, their pink outer layers used as often for colour as flavour. There are also evergreen, perennial varieties, such as Welsh and "everlasting" onions, grown for their green leaves.

Onions contain an irritant that stimulates the tear glands, some varieties more than others. Suggestions to counteract this effect whilst preparing onions include:

 skinning and cutting them under water
 breathing through the mouth
 using an electric fan
 wearing contact lenses or goggles
 using a very sharp knife to reduce cell damage
 cutting the root last, as it has the highest concentration of irritants.
Wide-ranging claims have been made for the curative and preventative effects of eating onions in ailments from heart disease to osteoporosis; they have also been used externally to treat boils, blisters and stings. In folklore they are used to forecast weather: thick skins mean a bad winter. Onion skins also make a traditional yellow dye.
Seed remains of onions have been found from 5000 BC. Ancient Egyptians revered their spherical shape and concentric rings as symbols of eternal life, ancient Greek athletes were fed onions to improve their performance, Roman gladiators rubbed down with them to firm up their muscles. In the Middle Ages onions were sometimes used to pay rent. Christopher Columbus took them to the Americas but found a native wild onion already growing there. Through much of the 20th century the arrival every summer of Breton onion sellers on bicycles heavily draped with onion strings was a fixture in the south of England - a museum dedicated to this Journee d'Albion was opened in Roscoff in 2003. In recent times many older varieties have been lost: a French seed catalogue of 1885 offered 74 varieties, a British one of 2003 only five.