`star` Seed
`star` Types of Fruits
`star` Advantages and Importance of Seeds
`star` Apomixis and Parthenocarpy


● In angiosperms, the seed is the final product of `color{Violet}"sexual reproduction"`.

● It is often described as a `color{Violet}"fertilised ovule"`.

● `color{Violet}"Seeds"` are formed `color{Violet}"inside fruits"`.

● A seed typically consists of `color{Violet}"seed coat"`(s), `color{Violet}"cotyledon"`(s) and an `color{Violet}"embryo axis"` or may or may not contain endosperm.

● The `color{Violet}"cotyledons"` of the embryo are simple structures, generally `color{Violet}"thick and swollen"` due to storage of food reserves (as in legumes).

● Mature seeds may be non-albuminous or albuminous.

`star` Non-albuminous seeds have `color{Violet}"no residual endosperm"` as it is completely consumed during embryo development (e.g., pea, groundnut).

`star` Albuminous seeds retain a part of endosperm as it is `color{Violet}"not completely used"` up during embryo development (e.g., wheat, maize, barley, castor, sunflower).

● Occasionally,in some seeds such as black pepper and beet, `color{Violet}"remnants of nucellus"` are also persistent.

● This residual, `color{Violet}"persistent nucellus"` is the `color{Violet}"perisperm"`.

● `color{Violet}"Integuments"` of ovules harden as tough protective `color{Violet}"seed coat"`.

● The `color{Violet}"micropyle"` remains as a `color{Violet}"small pore"` in the seed coat.

● This facilitates `color{Violet}"entry"` of `color{Violet}"oxygen"` and `color{Violet}"water"` into the seed during germination.

● As the `color{Violet}"seed matures"`, its water content is `color{Violet}"reduced"` and seeds become `color{Violet}"relatively dry"` (10-15 per cent moisture by mass).

● The general `color{Violet}"metabolic activity"` of the embryo `color{Violet}"slows down"`.

● The embryo may enter a state of `color{Violet}"inactivity"` called `color{Violet}"dormancy"`, or if favourable conditions are available (adequate moisture, oxygen and suitable temperature), they `color{Violet}"germinate"`.

● As `color{Violet}"ovules"` mature into `color{Violet}"seeds"`, the `color{Violet}"ovary"` develops into a `color{Violet}"fruit"`, i.e., the transformation of ovules into seeds and ovary into fruit proceeds simultaneously.

● The `color{Violet}"wall of the ovary"` develops into the wall of fruit called `color{Violet}"pericarp"`.


● The fruits may be `color{Violet}"fleshy"` as in guava, orange, mango, etc., or may be `color{Violet}"dry"`, as in groundnut, and mustard, etc.

● Many fruits have evolved mechanisms for `color{Violet}"dispersal of seeds"`.

● In most plants, by the time the `color{Violet}"fruit develops"` from the ovary, other floral parts `color{Violet}"degenerate"` and `color{Violet}"fall off"`.

● However, in a few species such as apple, strawberry, cashew, etc., the `color{Violet}"thalamus"` also contributes to `color{Violet}"fruit formation"`.

● Such fruits are called `color{Violet}"false fruits"`.

● Most fruits however develop only from the ovary and are called `color{Violet}"true fruits"`.

● Although in most of the species, fruits are the results of fertilisation, there are a few species in which `color{Violet}"fruits"` `color{Violet}"develop"` `color{Violet}"without fertilisation"`.

● Such fruits are called `color{Violet}"parthenocarpic fruits"`.

● `color{Violet}"Banana"` is one such example.

● Parthenocarpy can be `color{Violet}"induced"` through the application of `color{Violet}"growth hormones"` and such fruits are `color{Violet}"seedless"`.


● Seeds offer `color{Violet}"several advantages"` to angiosperms.

● Firstly, since reproductive processes such as pollination and fertilisation are `color{Violet}"independent of water"`, seed formation is more dependable.

● Also seeds have better `color{Violet}"adaptive strategies"` for dispersal to new habitats and help the `color{Violet}"species to colonise"` in other areas.

● As they have sufficient `color{Violet}"food reserves"`, young seedlings are `color{Violet}"nourished"` until they are capable of photosynthesis on their own.

● The `color{Violet}"hard seed coat"` provides protection to the young embryo.

● Being products of sexual reproduction, they generate `color{Violet}"new genetic combinations"` leading to variations.

● Seed is the `color{Violet}"basis"` of our `color{Violet}"agriculture"`.

● `color{Violet}"Dehydration"` and `color{Violet}"dormancy"` of mature seeds are crucial for `color{Violet}"storage of seeds"` which can be used as `color{Violet}"food"` through out the year and also to `color{Violet}"raise crop"` in the next season.

● The period for which the seeds remain `color{Violet}"alive"` after they are `color{Violet}"dispersed"`, varies greatly.

● In a few species the seeds `color{Violet}"lose viability"` within a few months.

● Seeds of a large number of species live for `color{Violet}"several years"`.

● Some seeds can `color{Violet}"remain alive"` for hundreds of years.

● There are several records of very `color{Violet}"old yet viable"` seeds.

● The oldest is that of a lupine, `color{Violet}"Lupinus arcticus"` excavated from `color{Violet}"Arctic Tundra"`.

● The seed germinated and flowered after an estimated record of `color{Violet}"10,000 years of dormancy"`.

● A recent record of `color{Violet}"2000"` years old `color{Violet}"viable seed"` is of the date palm, `color{Violet}"Phoenix dactylifera"` discovered during the archeological excavation at `color{Violet}"King Herod’s palace"` near the Dead Sea.


● Although seeds, in general are the products of fertilisation, a few flowering plants such as some species of `color{Violet}"Asteraceae and grasses"`, have evolved a special mechanism, to produce `color{Violet}"seeds without fertilisation"`, called `color{Violet}"Apomixis"`.

● Thus, apomixis is a form of `color{Violet}"asexual reproduction"` that `color{Violet}"mimics sexual reproduction"`.

● There are several ways of development of `color{Violet}"apomictic seeds"`.

● In some species, the diploid egg cell is formed without `color{Violet}"reduction division"` and develops into the embryo `color{Violet}"without fertilisation"`.

● More often, as in many `color{Violet}"Citrus and Mango"` varieties some of the `color{Violet}"nucellar cells"` surrounding the embryo sac start dividing, `color{Violet}"protrude"` into the embryo sac and develop into the embryos.

● In such species each ovule contains `color{Violet}"many embryos"`.

● Occurrence of `color{Violet}"more than one embryo"` in a seed is referred as `color{Violet}"polyembryony"`.

● Hybrid varieties of several of our food and vegetable crops are being extensively cultivated.

● Cultivation of hybrids has tremendously `color{Violet}"increased productivity"`.

● One of the problems of hybrids is that hybrid seeds have to be `color{Violet}"produced every year"`.

● If the seeds collected from `color{Violet}"hybrids are sown"`, the plants in the progeny will `color{Violet}"segregate"` and do not maintain hybrid characters.

● Production of hybrid seeds is `color{Violet}"costly"` and hence the cost of hybrid seeds becomes `color{Violet}"too expensive"` for the farmers.

● If these hybrids are `color{Violet}"made into apomicts"`, there is `color{Violet}"no segregation of characters"` in the hybrid progeny.

● Then the farmers can keep on using the `color{Violet}"hybrid seeds"` to raise new crop year after year and he does not have to buy hybrid seeds every year.

● Because of the importance of apomixis in hybrid seed industry, active research is going on in many laboratories around the world to understand the `color{Violet}"genetics of apomixis"` and to transfer `color{Violet}"apomictic genes"` into hybrid varieties.