Hibernation is a common phenomenon in animals. It is an extended period when an animal remains inactive or dormant due to unfavourable conditions such as bad weather during the winter.
Bats are still flying on mild early winter evenings but as winter progresses and grasps us in its chilly embrace, flies will become scarce forcing bats to retreat into hibernation.
Like animals, many plants 'hibernate' but among plants the phenomenon is called perennation. Since they are soft, plants bodies are prone to frost damage so to perennate many plants go through a profound change and morph into a form especially adapted to perennating. Such forms are called perennating organs.
The humble spud is a common example. If you think of a potato plant from the plant's point of view, it faces a problem as winter approaches: the shoot is likely to be damaged by frost. To ensure its survival, the plant has evolved the strategy of killing off its own soft green parts that are going to be useless during the winter anyway and storing all its energy in the lumps or perennating organs that we call potatoes.
The potato plant forms its perennating organs along portions of underground stems. The eyes on the spud are stem buds that will burst into life in spring as soon as the winter frosts have passed, sending up a soft new plant to flower and fruit.
Most perennating organs form underground as they use the surrounding protective covering of soil to stop them freezing. Any part of a plant can be adapted and can swell up as a perennating organ: carrots and parsnips are swollen tap roots, onions are hugely swollen buds. A tuber is a lump; potatoes are stem tubers whereas dahlias are root tubers.
Corms and bulbs are often confused. The only way to tell them apart is to cut them in half. A corm is part of a stem and is solid throughout; a bulb is a big bud, so it will have layers like an onion. Crocuses and gladioli are corms whereas daffodils and lilies are bulbs.
While perennation is especially common in winter, some plants do it in summer. Essentially, perennation is a means of avoiding unfavourable conditions. Bluebells, for example, growing in a woodland get shaded out when leaves open on the trees so they flower early in the spring and perennate as tree buds open and light conditions become poor to intolerable.