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what the line means "This event is a precursor to the seed habit considered an important step in evolution"?
Asked by rohitraman1115 | 07 Nov, 2019, 08:45: PM
Expert Answer
- 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.
- During the usual reproductive cycle in the heterosporous vascular land plants, the megaspores 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. The megaspore is permanently retained within the megasporangium.
- Here, within the confines of the megasporangium wall the megaspore germinates to form egg/zygote containing female gametophyte.
- 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.
- This event is of significant important and acts as a crucial step for the formation of seed habit.
- 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.
- The development and evolution of seed habit was a great success and a giant leap which ultimately enabled plants to colonize land permanently.
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