You may think that if a plant has an underground storage organ, that remains there year after year, pushing through the soil to flower such as lilies, crocus, cyclamen, erythronium, iris, daffodils lily of the valley and dahlias, then it must be a bulb.
But you would be wrong! Although some of these are true bulbs, the internal structures are quite different – if you look at where the buds and roots originate, and cut them in half you can see how they are all really either adapted stems or roots. We looked them up in a book to make sure - its a long time since I was at college...
· Bulbs – Modified stems, where the overlapping leaves have been adapted to swell and store food and nutrients for the plant eg. Lilies & Daffodils
· Corms –Stubby modified stems, which are vertically orientated eg. Crocus & Erythonium
· Rhizomes - Modified plant stems that grow near the soil surface and producing the upward shoot and downward root system eg. iris and lily of the valley.
Plants often modify themselves to ensure survival, and all these modifications occur to survive the British climate - when temperatures drop below freezing, the plant does not have to produce food using photosynthesis – it has plenty stored already for the next year.