`star` Introduction
`star` Classification
`star` Reproductive Structures
`star` Fertilisation and Development of seed and fruit


●In the angiosperms, the reproductive organs (pollen grains and ovules) are developed in specialized structures called flowers. Thus, these are called `color{Green}"Flowering plants"`.

●In angiosperms, the ovules are enclosed within the ovaries and hence the seeds are enclosed by fruits (`color{Green}"angio-covered; sperma-seeds"`).

●In them, the `color{Green}"vascular tissues"` are quite well-developed; with the xylem having vessels and the phloem having sieve tubes with companion cells.

●The angiosperms are an exceptionally large group of plants occurring in wide range of habitats.

●They range in size from tiny, almost microscopic 𝘞𝘰𝘭𝘧𝘪𝘢 to tall trees of 𝘌𝘶𝘤𝘢𝘭𝘺𝘱𝘵𝘶𝘴 (over 100 metres).

●They provide us with food, fodder, fuel, medicines and several other commercially important products.

● Important vegetative and reproductive parts of a flower are shown below:


They are divided into two classes: the Dicotyledons and the Monocotyledons based on the number of cotyledons within their seed.

Their differentiation is given below:


`color{brown}"Male Structures"`:

● `color{Green}"Stamens"` are the male sex organs in a flower.

● Each stamen consists of 2 parts; a slender `color{Green}"filament"` with an `color{Green}"anther"` at the tip.

● An anther contains `color{Green}"four microsporangia"`, where the microspore mother cells become differentiated.

● Then, the microspore mother cells undergo meiosis to produce four `color{Green}"microspores"`, each of which develops into a `color{Green}"pollen grain"`.

`color{brown}"Female Structures"`:

● The female sex organs in a flower are the `color{Green}"pisti"`l or the `color{Green}"carpel"`.

● Pistil consists of three parts, an `color{Green}"ovary"` (enclosing one to many ovules), a `color{Green}"style"` and a `color{Green}"stigma"`.

● Each ovule (megasporangium) has a body called `color{Green}"nucellus"`. It is covered by two `color{Green}"integuments"`, except at the micropyle.

● A `color{Green}"megaspore mother cell"` differentiates in the nucellus and it undergoes meiosis; eventually one functional megaspore enlarges and forms the highly reduced haploid female gametophyte, called `color{Green}"embryo sac"`.

● Each embryo-sac has a `color{Green}"three-celled egg apparatus – one egg cell and two synergids"`, `color{Green}"three antipodal cells"` and `color{Green}"two polar nuclei"`.

●The polar nuclei eventually fuse to produce a `color{Green}"diploid secondary nucleus"`.


● Pollen grains, after dispersal from the anthers, are carried by wind or various other agencies to the stigma of a pistil. This is termed as pollination.

● The pollen grains germinate on the stigma and the resulting `color{Green}"pollen tubes"` grow through the tissues of stigma and style and reach the ovule.

● The pollen tubes enter the embryo-sac where two male gametes are discharged.

● One of the male gametes fuses with the egg cell to form a zygote (`color{Green}"syngamy"`).

● The other male gamete fuses with the diploid secondary nucleus to produce the `color{Green}"triploid primary endosperm nucleus (PEN)"`.

● Because of the involvement of two fusions, this event is termed as `color{Green}"double fertilisation"`, an event unique to angiosperms.

● The zygote develops into an embryo (with one or two cotyledons) and the PEN develops into `color{Green}"endosperm"` which provides nourishment to the developing embryo.

● The synergids and antipodals degenerate after fertilisation.

● During these events the `color{Green}"ovules develop into seeds and the ovaries develop into fruit"`.

Below is the process of pollination and fertilisation: