Site author Richard Steane
The BioTopics website gives access to interactive resource material, developed to support the learning and teaching of Biology at a variety of levels.
Onions are in fact bulbs. They consist of many leaves wrapped around each other. Beneath this is a small disc - the equivalent of a stalk - from which roots sprout.
The leaves within the bulb which are usually white or partly red in colour contain stored food for the plant in order to survive through the winter and grow again and produce a flower the next year. Within these leaves is a chemical compound which deters some animals which might eat the food store, but this is what humans expect to find!
The outside layers of leaves become dry and protect the bulb inside. In the centre of the bulb are one or more buds and when the onion is planted in the ground (or sometimes before this) green leaves emerge and splay out on either side.
What is this 2 year lifecycle called?
What is the name given to the process of survival to the next year?
Many people do not realise that onions can produce flowers. Onion bulbs are usually harvested at the end of the first growing season, before they have a chance to bolt, i.e. use their energy in flowering and producing seeds.