StemsPart II

Fat and Starchy

Types of underground stems

• Can you think of something that you would call an underground stem besides bulbs?

Corms

Can you see anything that they have in common?

Definition• A solid, erect,

enlarged underground stem with leaves absent or dry and scalelike; usually below ground.

Can you find the differences between corms and bulbs

• Think of leaves and food storage

Answer

• Corms are starchy food storage organs, basically a swollen stem.

• Bulbs have bundles of leaves that store the food

• Corms might have one leafy covering, but not always

Life cycle

• At the beginning of the growing season, the food stored in the corm enables the terminal bud to grow rapidly and produce leaves and flowers above ground.

• Later in the year, food made by the leaves is sent back, not to the old corm, but to the base of the stem immediately above it. This region swells and forms a new corm on top of the old, now shrivelled, corm.

• Some of the lateral buds on the old corm have also grown and produced new plants with corms.

This allows the corm to grow in size from year to year.

Who said plants don’t move?

• The formation of new corms on top of the old one draws them closer to the soil surface

• Contractile roots on these pull the plant down as they contract.

• Since the corm is a stem, it has lateral buds which can grow into new plants. The stem remains below ground all its life, only the leaves and flower stalk coming above ground.

Some common corms• Many Arums– Taro – feeds millions of people all over the tropics• Poi

– Amorphophallus titanum, the largest inflorescence in the world

• Turnips• Beets• radish

Homework

• What corms would you like to see planted in our garden or greenhouse?– Look up how to store Calla lily corms– Find gardening techniques for beets, turnips and

radishes?– What would you need to grow Taro? Can it be

grown outdoors or do you need the greenhouse for this.

– Look up a recipe for poi or food with poi in it.