2. Identify the structure and types of leaves
All leaves originate as primordia in the
buds.
Leaves are attached to stems at nodes,
with stem regions between nodes
known as internodes.
Phylotaxy (leaf arrangement) generally
occurs in one of three ways: 1 -
Alternate 2 - Opposite 3 - Whorled
5. …..
leaves …..
Functions :
1 - produce food for the plant by
photosynthesis
2 - store food
3- transpiration (evaporation of water from the plant)
4 - gas exchange
5 - shading potential competitors
6 - protection and reproduction in certain
plants
6. There are four basic kinds
of leaves:
Simple leaves-have a flat, undivided blade that is supported by a
stalk called a petiole. The petiole is typically supported by collenchyma
and sclerenchyma fibers.
Compound leaves-have blades divided into leaflets that form in
one plane and lack axillary buds. Each compound leaf has a single bud at
the base of its petiole.
There are two kinds of compound leaves: pinnately compound and palmately
compound leaves. Pinnately form in pairs along a central stalklike rachis, and
palmately attach at the same point.
Peltate leaves-have petioles that attach to the middle of the blade.
Perfoliate leaves-are sessile leaves that surround and are
pierced by the stems.
7. Modified leaves
Tendrils
Stipules
Spines
Bud Scales
Bracts
Window leaves
Storage leaves
Insect-trapping leaves
Leaves modified for reproduction
Cotyledons
Prophylls
Like other organs,
leaves are often
modified for
functions other
than
photosynthesis.
8. tendrills
Tendrils-of plants are leaves modified for support. In some
plants the entire leaf is a tendril; photosynthesis in these
plants is delegated to leaflike structures called stipules at
the base of each leaf. Tendrils, of many plants may be up to
30 cm long, which makes them well suited for seeking
support in the plant's nearby environment.
10. Stipules
are small, leaflike
structures at the base of
petioles, and have a
variety of functions. Some
are photosynthetic, while
others form protective
spines.
Stipule in rose
16. Bud Scales
are tough, overlapping, waterproof leaves that
protect buds from frost, desiccation, and
pathogens. Bud scales form before the onset of
unfavorable growing seasons ie winter.
17. Window leaves
are common in many desert plants, are shaped
like tin ice-cream cones and grow mostly
underground, with only a small transparent
"window" tip protruding above the soil level.
18. Bracts (Floral Leaves)
are floral leaves that form at the base of a flower
or flower stalk. They are usually small and
scalelike, and protect developing flowers.
19. Storage leaves
flowerpot leaves are typically of rosette plants,
and such epiphytes. They are packed tightly into
a flowerpotlike structure that catches falling
water and debris.
20.
21. Insect-trapping leaves
in carnivorous plants, leaves modified for
attracting, trapping, and digesting animals. These
adaptations range from sticky flypaper surfaces
to vatlike leaves.
26. Leaves modified for reproduction
-form tiny plants at the edges of their leaves.
These plants become new individuals when they
are shed from parent leaves.
29. Prophylls
are the first leaves to form on axillary buds.
Monocots have one usually, where dicots have
two, suggesting that tiny leaves may be
analogous to cotyledons. Prophylls protect
axillary buds.
30. Shade Leaves
Leaves in the
shade receive less
total light, thus
tend to be thinner
and have fewer
hairs than leaves
on the same tree
exposed to direct
light.
31. Leaves of Arid Regions
Many have thick, leathery leaves and
few stomata. Some have succulent,
water-retaining leaves, or dense, hairy
coverings.
