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Flowers

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Plants and People
Flowers
Why a Flower?
The Reproductive Structure of
Flowering Plants:
Perianth
Petal: Corolla
Sepal:Calyx
Flower Anatomy
Calyx: the outer whorl of sepals;
typically these are green, but are
petal-like in some species.
Flower Anatomy
Corolla: the whorl of
petals, which are usually
thin, soft and colored to
attract animals that help
the process of pollination.
The coloration may
extend into the ultraviolet,
which is visible to the
compound eyes of insects,
but not to the eyes of
birds.
Flower Anatomy
Androecium (from Greek
andros oikia: man's house):
one or more stamens, each
with a filament topped by an
anther where pollen is
produced.
Pollen contains the male
gametes.
Flower Anatomy
Gynoecium (from Greek gynaikos oikia: woman's
house): all the female parts—the pistil(s) with
ovule(s) inside.
Flower Anatomy
The basic unit of the female reproductive
structure is the carpel. Each physcial body is
called a pistil.
A flower may have a single carpel, which is a
simple pistil (unicarpellate), or several carpels
united in one compound pistil (syncarpous), or
a cluster of un-united carpels/pistils
(apocarpous)
The sticky tip of the pistil, the stigma, is the
receptor of pollen.
The supportive stalk, the style, becomes the
pathway for pollen tubes to grow from pollen
grains adhering to the stigma, to the ovules,
containing the gametes, housed inside the
ovary.
Flower Anatomy
carpel
fertilization
carpel structure
Evolution of the Carpel
See figures 3.1 and 3.2 in your book
Fruit and Seed Formation
A fruit develops from an ovary. A seed develops from an ovule.
Flower Structure Variation
perfect
imperfect
imperfect
Flower Structure Variation
Ovary Position
A. ovary superior, floral parts hypogynous
B. ovary inferior, floral parts epigynous
C. ovary half-inferior
D. ovary superior, floral parts perigynous, hypanthium cup shaped
Flower Structure Variation
A flower having sepals, petals, stamens, and pistils is
complete; if a flower is lacking one or more of these
whorls, it is said to be incomplete.
complete
incomplete
no stamens present = incomplete
Inflorescences
An inflorescence is a group or cluster of flowers. It
may be branched or unbranched. Modifications can
involve the length, variations in the proportions,
compressions, and swellings, and the order in which
the flowers open.
Usually the modifications have been evolved to
optimize the plant’s method of pollen dispersal.
Inflorescences
raceme
spike
corymb
umbel
Inflorescences
spadix
head
catkin
Pollen Dispersal by Animals
Bees, Beetles, Bats, Birds, Butterflies, etc…
Symmetry
Flowers that are actinomorphic have
"radial symmetry", meaning they can be
divided into symmetrical halves by more
than one longitudinal plane passing through
the axis, much as a pie can be cut into
several equal and identical pieces.
Zygomorphic flowers are "yoke shaped”
or have"bilateral” symmetry, where
flowers can be divided by only a single
plane into two mirror-image halves, much
like a yoke or a person's face.
Dicot versus Monocot
Dicot
Monocot
Lab Objectives
1. Flowers are arranged in groups called inflorescences. We will examine some
inflorescences particular to certain families later in the semester. For now,
know what an inflorescence is and which ones we looked at today.
2. DRAW a longitudinal section of a typical flower labeling the following parts:
receptacle, calyx, sepals, corolla, petals, perianth, pedicel, ovary, ovule, style,
stigma, pistil, gynoecium, anther, filament, stamen, and androecium.
3. EXAMINE by dissection the floral material provided making long and cross
sections of the flower and its parts. On a separate sheet of paper, SKETCH the
flowers and label the parts. Then, FOR EACH FLOWER, answer the following
questions:
A. Is the flower actinomorphic (regular) or zygomorphic (irregular)?
B. How many sepals are present? Petals? Stamens? Carpels? To count carpels,
count the locules, styles, style branches, and/or the zones of placentation by
cross- sectioning the ovary.
C. Is the ovary inferior or superior?
D. Is the flower from a monocotyledonous or dicotyledonous plant?
E. Is the flower perfect (both sexes present) or imperfect? Complete (all four
floral whorls) or incomplete?
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