Significance of seeds and fruits:

The seeds are the most efficient propagules produced by the plants.

The distribution and dominance of Angiosperms on the earth (conquest of land by Angiosperms) is due to the seeds.

Success of seeds as propagule is due to many characteistics of seeds as follows.

 

Dormancy -

It is temporary suspension of growth. One of the factors which control dormany is presence of certain growth inhibitors in the seeds which prevent germination. Duing this period, seeds are dispersed at different places. (Zygote produced by Cryptogams, germinates immediately).

 

Viability-

It is the functional ability of seeds to germinate after considerable dormancy period. Germination can be delayed till the onset of favourable conditions.

 

Reserve food -

Fully developed embryo is nourished by food stored in either endosperm or cotyledons during germination of seed and a seedling is produced.

 

Protective coat -

Testa, the outer, hard seed coat, gives protection against the mechanical shocks, fluctuations in temperature and dry conditions. Animals eat fruits and either throw away seeds or if are consumed, they are not digested due to the hard seed coat and are removed through excreta.

 

Dispersal -

Some seeds produce various structures like wings, pappus calyx (persistent and hairy), hooks or sticky substances, and seeds are actively or passively transported to distant places.

 

Edible fruits -

Many fruits are consumed by different organisms and seeds are thrown. Thus development of fruits and seeds play signiicant role in the spread of the species.

 

Summary

• In Angiosperms. reproduction is of two types; asexual reproduction-which does not involve the fusion of gametes and sexual reproduction, which involves the fusion of gametes.
• Asexual reproduction occurs naturally through the vegetative parts like roots, stem, leaves and buds. This method preserves the genetic characters of parent in the daughter plants. It mostly occurs through the modified roots and stem. In some plants through leaf (e.g. Bryophyllum).
• Artificial vegetative propagation is done with the help of methods like cutting, grafting and budding. The vegetative propagation is a cheap method of multiplication and useful for cultivating the plants like banana, pineapple and grapes. It also helps in production of clones of economically useful and rare plants.
• Sexual reproduction takes place by the formation of highly specialized organs called flowers.
• Events involved in this process are; development of male gametophyte, development of female gametophyte, pollination, double fertilization development of endosperm and embryo and formation of fruits and seeds.
• Anther of stamen and ovule in the ovary produce microspores and megaspores which develop into male and female gametophytes respectively.
• Development of male and female gametophytes is endosporic.
• Male gametophyte is formed by the pollen grain and is highly reduced. Mature male gametophyte consists of degenerating tube neucleus and two male gametes in the pollen tube.
• The female gametophyte or embryo sac is monosporic, seven celled and eight nucleated.
• Pollination is the transfer of pollen grains from anther to the stigma. This process may be achieved by using different types of biotic and abiotic agencies.
• Double fertilization is achieved by siphonogamy to form a diploid zygote and triploid primary endosperm nucleus.
• The primary endosperm nucleus develops into a triploid nutitive tissue called endosperm. The diploid zygote develops to form an embryo.
• Fertilized ovule after embryo and endosperm development, changes into a seed and the ovary forms a fruit.