In the autumn (or in spring, in the case of overwintering onions), the foliage dies down and the outer layers of the bulb become more dry, and brittle.

As a food item, they are often served raw as a vegetable or part of a prepared savoury dish, but can be eaten cooked or used to make pickles or chutneys.

[6] Synonyms during its taxonomic history are:[7][8] A. cepa is known exclusively from cultivation,[9] but related wild species occur in Central Asia and Iran.

[16] It has an affinity with Spanish: cebolla, Italian: cipolla, Polish: cebula, and the German Zwiebel (this last altered by folk etymology).

[26] The Assyriologist and "gourmet cook"[26] Jean Bottero stated this was "a cuisine of striking richness, refinement, sophistication and artistry".

[26] Ancient Egyptians revered the onion bulb, viewing its spherical shape and concentric rings as symbols of eternal life.

He documented Roman beliefs about the onion's ability to improve ocular ailments, aid in sleep, and heal everything from oral sores and toothaches to dog bites, lumbago, and even dysentery.

Archaeologists unearthing Pompeii long after its 79 AD volcanic burial have found gardens resembling those in Pliny's detailed narratives.

They found close relatives of the plant such as Allium tricoccum readily available and widely used in Native American gastronomy.

[32] Onions pickled in vinegar are eaten as a side serving with traditional pub food such as a ploughman's lunch.

Forming a single layer of cells, the bulb epidermis is easy to separate for educational, experimental, and breeding purposes.

[40] Most onion cultivars are about 89% water, 9% carbohydrates (including 4% sugar and 2% dietary fibre), 1% protein, and negligible fat (table).

[43] Like garlic,[44] onions can show an additional colour – pink-red – after cutting, an effect caused by reactions of amino acids with sulfur compounds.

[47] Symptoms can include contact dermatitis, intense itching, rhinoconjunctivitis, blurred vision, bronchial asthma, sweating, and anaphylaxis.

This gas is produced by a chain of reactions which serve as a defence mechanism: chopping an onion causes damage to cells which releases enzymes called alliinases.

[49] Leaving the root end intact also reduces irritation as the onion base has a higher concentration of sulphur compounds than the rest of the bulb.

[59] Synthetic onion lachrymatory factor has been used in a study related to tear production,[60] and has been proposed as a nonlethal deterrent against thieves and intruders.

Southern European and North African varieties are often known as "intermediate-day" types, requiring only 12–13 hours of daylight to stimulate bulb formation.

[67] Hot temperatures or other stressful conditions cause them to "bolt", meaning that a flower stem begins to grow.

[67][69] In suitable climates, certain cultivars can be sown in late summer and autumn to overwinter in the ground and produce early crops the following year.

[18] Routine care during the growing season involves keeping the rows free of competing weeds, especially when the plants are young.

[71] The larvae of the onion leaf miner or leek moth (Acrolepiopsis assectella) sometimes attack the foliage and may burrow down into the bulb.

[73] The onion eelworm (Ditylenchus dipsaci), a tiny parasitic soil-living nematode, causes swollen, distorted foliage.

The bases of the bulbs are attacked and become covered by a fluffy white mass of mycelia, which later produces small, globular black structures called sclerotia.

No cure for this fungal disease exists, so affected plants should be removed and destroyed and the ground used for unrelated crops in subsequent years.

[12] The range of diversity found among these cultivars includes variation in photoperiod (length of day that triggers bulbing), storage life, flavour, and skin colour.

Tops die back in the heat of summer and may return with heavy rains; bulbs can remain in the ground or be harvested and stored in a cool dry place for planting in the fall.

The "wondrous creature, a joy to women" stands "in a bed"; "My column is erect and tall"; a woman "rubs me to redness" but at once "she feels my meeting"; the riddle ends "Wet will be that eye.

[91] R. Drew Griffith comments that the double comparison of the tunic that Penelope gave to the disguised Odysseus to onion and sun "risks being funny", and notes that Theopompus indeed found it "ridiculous".

[92] Griffith suggests that Homer included the onion because of its capacity to produce tears, hinting at Penelope's sorrow at Odysseus's long absence.