One of the main characteristics of higher plants is that they
reproduce by means of seeds. There are two
major groups of seed-producing plants: Gymnosperms and Angiosperms. The
Gymnosperms
include the common cone-bearing evergreens
such as pine, spruce, and fir, in which the seeds are naked and not enclosed
within fruits. The Angiosperms or flowering
plants have seeds covered by or enclosed within the fruit.
The characteristic reproductive structures of the Angiosperms are the
flowers.
Morphologically, a flower represents a highly modified stem which bears
specialized leaves forming the so-called floral organs. There is wide variation
among flowers of different plants with respect to the kinds, numbers, size,
form, and arrangement of the floral organs. Some of the floral organs later
develop into fruit. There is as much variety in the types of fruits as
in the flowers from which they are produced.
In this exercise you will examine the parts of flowers and some of the
different types of fruits that are produced by flowering plants.
GENERAL
INFORMATION
Fertilization, Seed and Fruit Development
The pollen, or male gametophyte (gamete-producing plant ) and the ovule,
or female gametophyte, represent the sexual generation in the life-cycle
of the flowering plant. The pollen may be transferred to the stigma of
the same flower or to the stigma of another flower of the same species.
In the former case the process is called self-pollination,
in the latter case, cross-pollination.
On the stigma, the pollen germinates , and produces the male gametes
which are transported to the ovule in a pollen tube. One of these
male gametes fuses with the female gamete within the ovule. This fusion,
called fertilization, marks the beginning
of the development of the embryo plant.
The tissues of the ovule surrounding the embryo form the seed,
while the tissues of the ovary, sometimes with some of the surrounding
structures, form the fruit. The fruit is the ripened
ovary (ovaries) with the enclosed seeds, if any, and in some cases
may include other parts of the parent flower. The characteristics of the
fruit are thus closely related to the characteristic of the flower (or
flowers), and especially the ovary (or ovaries) from which it was produced.
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