UNIT VI

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