Question

Discuss the development of seed habit

Answer 1

Hint: Seeds are ovules formed after fertilization. A seed consists of an embryo, stored food or nutrition, and a seed coat. Seed habit is one of the most complex and successful methods of sexual reproduction.

Complete answer:
Seed habit is considered as an adaptation of heterospory, and retention and germination of a single megaspore within the megasporangium. The seed plants, which include gymnosperms and angiosperms account for the maximum diversity in the vascular plants. This is because they have an adaptive advantage in the form of seeds.
The origin and evolution of seed habitation started to occur in the late Devonian period, about 385 million years ago. It began with the evolution of the first modern tree, Archaeopteris species which produced an advanced system of spores called heterospory.

Additional Information:
 The precursors or conditions for the evolution of seed were:
-Evolution of heterospory: It is the development of separate male microspores and female megaspores.
-Evolution of integuments: It is a type of maternal tissue that protects the ovule. The integument in the ovule develops to form the seed coat for the seeds.
-Evolution of pollen receiving structures: This marked the transition towards water independence, i.e. non-dependence on the water for fertilization. Instead, a specialized pollen receptacle was evolved.

Note: -Seeds are a characteristic feature of the spermatophytes which includes the gymnosperms and angiosperms.
-Though seeds started evolving in the gymnosperms, the evolutionary relationships between the gymnosperm lineages are not very well known.
-Before the development of proper seeds, some ferns with heterospory showed the development of cupules. They were pre-ovule-like structures without integuments and were dependent on water for fertilization.
-After the development of seeds in gymnosperms, the angiosperms evolved the habit further and developed a soft fleshy protective covering for the seeds called the fruits which also help in the seed dispersal.