Question

The heterosporous pteridophytes show certain characteristics, which are precursors to the seed habit in gymnosperms. Explain.

Answer 1

Definition of heterospory:

Heterospory is defined as the production of two types of spores which differ in size (morphologically), origin and other aspects like function, by the same sporophytic land plant.

Characteristics of plants with seed habit:

The following are the characteristics leading to seed habit:-

● Heterospory: The production of two types of spores, i.e., microspores and megaspores.

● Retention of the megaspore in the megasporangium.

● The delivery of sperm to egg efficiently in a protective environment.

● Protection of the embryo by seed coat and inhibition of germination till a favourable environment is present.

Pteridophytes vs Gymnosperms:

Pteridophytes like Selaginella have achieved the first two steps of seed habit only. On the other hand, all the steps are achieved by gymnosperms. This shows that in the evolutionary sequence pteridophytes are the precursor to gymnosperms with respect to seed habit.