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.
(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.