The Shoot: Primary Structure
and Development
Chapter 25
True or False
1) Shoots contain stems
and leaves.
2) Shoots are the above
ground portion of the
plant and are
anatomically the same
as roots.
The Shoot
• Shoot- the above ground portion of the
plant, consisting of stem and leaves.
– Stem- the above ground axis of
vascular plants.
– Leaf- the principle lateral appendage
of the stem.
• Foliage leaf- photosynthetic organ.
• Node- the part of the stem where
one or more leaves are attached.
• Internode- the region of the stem
between two successive nodes.
• Bud- an embryonic shoot protected
by young leaves.
Primordium- a leaf or bud in its earliest stage of differentiation.
Pith- the ground tissue occupying the center of a root or shoot.
Pith- the ground tissue occupying the center of a root or shoot.
Basswood
Alfalfa
Corn
Modified Stems
• Tendrils- modified leaves that spirally coil and
aid in stem support.
• Stolons- runners; stems that grow horizontally
on the soil surface, often giving rise to new
plants at the nodes.
• Thorns- hard, woody, sharp-pointed modified
stems, arise from the axils of leaves.
• Spines- hard, woody, sharp-pointed modified
leaves or leaf-parts.
• Prickles- a small non-woody, sharp-pointed
outgrowth of bark or the epidermis.
True or False. This is a tendril.
True or False. This is also a tendril.
Given: the following is
a hard, woody,
sharp-pointed
modified stem that
arises from the axils
of leaves.
True or False.
This is a spine.
Spines
Prickles
Underground Stems
• Rhizome- a horizontal stem that grows at or below the
soil surface.
• Tuber- an enlarged, short, fleshy underground stem,
forms at the tip of a rhizome. i.e. Potato.
• Bulb- a shortened underground stem covered by
enlarged fleshy storage leaves. i.e. Onion and garlic.
• Corm- a thickened underground stem with small papery
leaves. i.e. Gladiolus and Crocus.
Leaf Arrangement
• Phyllotaxy- the arrangement of leaves on a stem.
– Basal- leaves are attached to an underground stem or
rhizome.
– Opposite- 2 leaves attached at each node, borne on
opposite sides of the stem.
– Alternate- 1 leaf attached at each node.
– Whorled- 3 or more leaves at each node.
Basal
Leaf Morphology
• Blade- lamina.
• Petiole- stalklike portion.
• Stipules- scalelike or leaflike
appendages at the base of leaves.
• Simple vs. Compound Leaves
– Simple- blades undivided.
– Compound- blades divided into
leaflets.
• Pinnately compound- leaflets arising
from both sides of the axis.
• Palmately compound- leaflets diverge
from the tip of the petiole.
Leaf Histology
• Mesophyll- the
ground tissue of the
leaf, specialized for
photosynthesis.
– Palisade parenchymaupper cells.
– Spongy parenchymalower cells.
Hydrophyte- waterlily.
Xerophyte- oleander.
Eudicot- random stomata.
Monocot- parallel stomata.
Leaf Abscission
• Abscission- the normal
separation of the leaf from
the stem.
• Structural and chemical
(ethylene) changes result in
the formation of an
abscission zone:
– Separation layer
– Protective layer
• Magnesium ions, sugars,
amino acids.