In bryophytes the male sex organ is antheridium and female sex organ is archegonium. The gametophyte ( n ) in bryophyte bears the primiture sex organs in the form of antheridium (male) which produce flagellate antherozoids which are male gamete and need thin film of water to swim and reach female reproductive organ (archegonium).

Archegonia is female part which has single egg cell. Both these reproductive parts are born on male and female, anthridiophore and archegoniophores borne on haploid gametophyte.

Bryophytes are amphibian of plant kingdom. It is a group of primitive plant having a dominant gametophytic plant body. These plants can live in soil but depend on water for movement of male gametes called antherozoids to reach archegonium (female organ having egg cell) so that fertilisation can take place.

The structure are as given

Heterospory is production of spores of two different sizes and sexes by the sporophytes of land plants. Two types of spores are produced by heterosporic plants.

Small spores are microspores which germinate into male gametophyte and large spores are macrospores which develop into female gametophyte.

In evolution of plants pteridophytes are intermediate between bryophytes and gymnosperms. All bryophytes are homosporous and all gymnosperms are heterosporous. This condition is advanced as sexual dimorphism result in cross fertilisation.

Primitive or earlier pteridophytes are homosporous later pteriodophytes are heterosporous e.g., Dryopteris, Pteris-homosporous Selaginella, Salvinia-heterosporous.

Seed habit The differentiation of spores into microspores and megaspores and their dependence on the parent sporophyte for the nutrition, are the certain features in the life cycle of Selaginella, which have been considered as the essential pre-requite for formation of seed, the characteristic of spermatophyte.

The evolution of heterospory and seed habits in Selaginella is evident by the following characters

(i) Reduction to a single functional megaspore per sporangium.

(ii) Retention and germination of megaspore within megasporangium

(iii) Development of protective layer and nutritive tissue called tapetum is present.

(iv) Development of embryosac with in the sporangium.

(v) Modification of distal end of mega sporangium to capture pollen grain.

(vi) Pollination and siphonogamy.

(vii) Temporary suspension of growth of embryo (dormancy period).