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.