What is heterospory ? Briefly comment on its significance

Heterospory is the production of two kinds of spores in pteridophytes E.g., Salvinia and Selaginella produces two kinds of spores (i) macrospores: these are large in size, (ii) microspores : these are small in size. These pteridophytes are heterosporous.
Significance:
(a) The mega and microspores germinate and then give rise to male and female gametophytes.
(b) The female gametophyte is retained on parent sporophyte for variable period of time.
© The development of zygote into young embryo occurs within female gametophyte.