Stem and Root Modifications

Floral Careers Plant Propagation

What Exactly is a Stem?Before we go any further in this

presentation, let’s define a stem.A stem:

is generally considered to be the central axis of the plant.

supports the leaves and flowers of a plant. has nodes from which new shoots and

sometimes new roots can arise. is usually found above-ground, but can be modified and found below-ground as well.

Stem Modifications

The following are stem modifications: Tubers Corms Bulbs Rhizomes Stolons

Tubers

A tuber is an underground stem that stores food.

We know a potato is a tuber because it has nodes (eyes) which produce new shoots.

A potato is a tuber

Corms

A corm is a swollen, vertical stem with a papery covering.

Gladiolus and Crocus are examples of plants that form corms.

Crocus corms

Corm Growth Cycle

Gladiolus corms with cormels

Bulbs

Bulbs come in 2 basic types: Tunicate bulbs; onions and tulips are examples. Scaly bulbs; tiger and asiatic lilies are

examples.

Tunicate Bulbs

Tunicate bulbs have: A papery outer

covering called a tunic. A compressed,

modified stem with nodes, called a basal plate.

Fleshy scales made of modified leaf tissue.

A tunicate bulb

Tunicate Bulbs

Fleshy Scales

Basal Plate

Onion is a tunicate bulb

Tunicate Bulbs

Tunicate bulbs form “onion rings” when cut in cross-section.

Onion bulb shown in cross-section

Scaly Bulbs

The other type of true bulb is a scaly bulb. Scaly bulbs: Lack a papery covering (tunic). Have a basal plate. Have fleshy scales made of leaf tissue. Do not form “onion rings” when cut in cross-

section.

Scaly Bulbs

Lilium is a scaly bulb

Bulb Growth Cycle

Rhizomes

Rhizomes are: underground stems. horizontally-growing. produce shoots and

adventitious roots.

Iris rhizome

Rhizomes

Some plants, like quack grass, produce long, thin rhizomes.

Quack Grass

Rhizomes

Other plants, like ginger, produce large, thick rhizomes called pachymorphs.

The pachymorph rhizome of Ginger

Stolons

Stolons are: Aboveground stems. Grow horizontally. Produce shoots and adventitious roots. Strawberry and Spider Plant are examples of

plants that produce stolons.

Stolons

Wild Strawberry stolons

Root Modifications

There are 2 basic types of root modifications: Fleshy Tap Roots Tuberous Roots

Fleshy Tap Roots

Carrots, beets, and radishes are examples of plants forming fleshy tap roots.

Carrots

Tuberous Roots

Sweet potato is an example of a tuberous root.

A sweet potato is a tuberous root

Tuberous Roots

Dahlias are perennial bedding plants that form tuberous roots.

Dahlia

End