One of the most significant events in the history of land plants was the development of seed habit. It was an important change in the reproductive system of the vascular plants which occurred approximately 390 million years ago.

Keywords Heterospory, megagametophyte, integument, sporophyll, micropyle, siphonogamy, Carboniferous, lepidodendrids, lateral laminae, radiospermic, cupule. 2 One of the most important events in higher vascular plant evolution is the evolution of Seed Habit. The origin and subsequent evolution of. Download PDF Download. Further studies into the molecular mechanisms underlying such processes might help us trace the molecular evolution of the seed habit even further. Recommended articles Citing articles (0). BanksSelaginella and 400 million years of separation.

First complete seeds appeared approximately 365 million years ago during late Devonian times. Technically a seed may be defined as a fertilized ovule. An ovule is an integument indehiscent megasporangium.

Integuments are specialized protective coverings around megasporangium which vary in number. All seed producing plants are called spermatophytes. Various steps involved in the evolution of seed habit are as follows.

• Evolution of heterospory. • Retention and germination of megaspore within the megasporangium. • Development of protective layers around megasporangium. • Reduction to a single functional megaspore per sporangium.

• Development of an embryo sac within the sporangium. • Modification of distal end of megasporangium for pollen capture. Evolution of heterospory. During the usual reproductive cycle in the heterosporous vascular land plants, the megaspores are used to be shed and dispersed soon after their formation in order to germinate into female gametophyte.

However in some plants ( e.g. Selaginella) the megaspore is not allowed to escape from megasporangium immediately after its formation.

In others the megaspore is permanently retained within the megasporangium. Here, within the confines of the megasporangium wall the megaspore germinates to form egg containing female gametophyte. Development of protective layers around megasporangium. Some branch like structure of sporophyte surrounding the megasporangium fused around to megasporangium to form protective envelope or integument. The megasporangium tightly locked by integuments becomes totally indehiscent.

This important change led to the evolution and formation of the ovule, which is nothing but an integumented indehiscent megasporangium. In this way more protection is accorded to the egg-containing apparatus in terrestrial environment.

Reduction to a single functional megaspore per sporangium. Pollen after being trapped in the distal cavity of the megasporangium produces pollen tube which carry male gametes deep into the embryo sac to fertilize the egg, forming a zygote, that forms an embryo. The megasporangium (ovule) after fertilization is transformed into a seed, the integuments becoming the seed coats.

The seed offers maximum degree of protection to a developing embryo under the unfavorable terrestrial environment. Ghost protocol full movie. The development and evolution of seed habit was a great success and a giant leap which ultimately enabled plants to colonize land permanently.