实验花的构造教学教案.ppt

第五章 植物器官的结构及组织分化
四、花
Flower
The duckweeds (family Lemnaceae) are
the smallest flowering plants; thei then be referred to as tepals.
Note that the sepals are attached to the
receptacle below the petals.
(b) A partly
dissected flower with two tepals and two
stamens removed to reveal the ovary.
The gynoecium consists of the ovary,
style, and stigma. The stamen consists of
the filament and anther. Note that the
sepals, petals, and stamens are attached
to the receptacle below the ovary, which
is made up, in the lily flower, of three
fused carpels. Such a flower is said to
be hypogynous.
The wall of the pollen grain serves to
protect the male gametophyte on its often
lIozardous journey between the anther
and the stigma. The outer layer, or exine,
is composed chiefly of a substance known
ossporopollenin, which appears to be a
polymer composed chiefly of carotenoids.
The exine, which is remarkably tough
atld resistant, is often elaborately
~culptured.
The sculpturing of pollen grain walls
is very precise and distinctly different
from one species to another, as revealed
ill these scanning electron micrographs
of pollen grains. (a) Pollen grains of the
horse chestnut (Aesculus hippocasta-
num). The pore of each grain through
which a pollen tube may emerge is vis-
ible in the furrow. (b) Pollen grains of
a lily (Lilium longiflorum). (c) Detail
of the surface of a lily (L. longiflorum)
pollen grain. (d) Pollen grain of the
western ragweed (Ambrosia psilosta-
chya). The pollen of ragweed is a
primary cause of hay fever. Spiny pollen
grains such as these are common among
members of the sunflower family, Aste-
raceae, of which ragweed is a member.
Mature pollen grain of Lilium, contain-
ing a two-celled male gametophyte. The
spindle-shaped generative cell will divide
mitotically, giving rise to two sperm; the
larger tube cell, which contains the gen-
erative cell, will form the pollen tube.
The round structure above the generat