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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:
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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:
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Tubers
Corms
Bulbs
Rhizomes
Stolons
Tubers
A potato is a tuber
 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.
Corms
Crocus corms
 A corm is a swollen,
vertical stem with a
papery covering.
 Gladiolus and
Crocus are examples
of plants that form
corms.
Corm Growth Cycle
Gladiolus corms with cormels
Bulbs
 Bulbs come in 2 basic types:
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Tunicate bulbs; onions and tulips are examples.
Scaly bulbs; tiger and asiatic lilies are
examples.
Tunicate Bulbs
 Tunicate bulbs have:
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A tunicate bulb
A papery outer
covering called a tunic.
A compressed,
modified stem with
nodes, called a basal
plate.
Fleshy scales made of
modified leaf tissue.
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:
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Lack a papery covering (tunic).
Have a basal plate.
Have fleshy scales made of leaf tissue.
Do not form “onion rings” when cut in crosssection.
Scaly Bulbs
Lilium is a scaly bulb
Bulb Growth Cycle
Rhizomes
 Rhizomes are:
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Iris rhizome
underground stems.
horizontally-growing.
produce shoots and
adventitious roots.
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:
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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:
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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