angiosperms v primary growth: leaves. leaf morphology n leaves are arranged on stems in either an...
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Leaf Morphology
Leaves are arranged on stems in either an opposite, alternate, or whorled pattern
This arrangement is called the phyllotaxis
Most leaves are either simple or compound
A SIMPLE LEAF
External Leaf Morphology
The leaf blade is connected to the stem by the petiole
Other leaf parts include: base, margin, apex, venation
margin
apex
base
venation
petiole
Pinnately compound leaves are similar to ferns: leaflets attached along a rachis
Palmate leaves have leaflets attached at one point
CompoundLeaves
Simple vs. Compound Leaves
Axillary buds occur at the base of each leaf - not at the base of leaflets
The abscission layer forms at the base of the leaf’s petiole - not at the base of a leaflet
Leaflets are generally all produced in the same plane - leaves have a phyllotaxis
Internal Structure (monocot)
Upper epidermis
Bulliform cells
Mesophyll Veins with
bundle sheath cells
Guard cells
Leaf Abscission
Abscission takes place at the base of the leaf (not leaflets)
Response to hormones triggered by environment changes
Two regions:– Separation layer– Protective layer
Variations and Uses
Multiple epidermal layers Thick cuticles Many trichomes (African
violet) Stomata in sunken pits with
trichomes (xerophytes) Stomata only on the upper
surface (water lilies) Leaves modified to be tendrils
or spines
Variations and Uses (cont.)
Carnivorous plants (specialized for obtaining mineral nutrients in wet or mineral poor habitats)– Venus fly trap– Sundew– Pitcher plants
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