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
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
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