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

Following are the character which are assumed to be precursors of seed habit & helped it in the evolution.

i) Evolutionary heterospory

ii) In-situ development of embryo within the female gametophyte.

iii) Decrease in number of megaspore to one.

iv) Apex of megasporangium modified for reception of pollen.

v) Megasporium got enveloped by integements.