<P> However , in some other groups , either the sporophyte or the gametophyte is very much reduced and is incapable of free living . For example , in all bryophytes the gametophyte generation is dominant and the sporophyte is dependent on it . By contrast , in all modern vascular land plants the gametophytes are strongly reduced , although the fossil evidence indicates that they were derived from isomorphic ancestors . In seed plants , the female gametophyte develops totally within the sporophyte which protects and nurtures it and the embryo sporophyte that it produces . The pollen grains , which are the male gametophytes , are reduced to only a few cells ( just three cells in many cases ) . Here the notion of two generations is less obvious ; as Bateman & Dimichele say `` ( s ) porophyte and gametophyte effectively function as a single organism '' . The alternative term ' alternation of phases ' may then be more appropriate . </P>
<P> However , in some other groups , either the sporophyte or the gametophyte is very much reduced and is incapable of free living . For example , in all bryophytes the gametophyte generation is dominant and the sporophyte is dependent on it . By contrast , in all modern vascular land plants the gametophytes are strongly reduced , although the fossil evidence indicates that they were derived from isomorphic ancestors . In seed plants , the female gametophyte develops totally within the sporophyte which protects and nurtures it and the embryo sporophyte that it produces . The pollen grains , which are the male gametophytes , are reduced to only a few cells ( just three cells in many cases ) . Here the notion of two generations is less obvious ; as Bateman & Dimichele say `` ( s ) porophyte and gametophyte effectively function as a single organism '' . The alternative term ' alternation of phases ' may then be more appropriate . </P>
in terms of alternation of generations the pollen grains
in terms of alternation of generations the pollen grains
are reduced to only a few cells ( just three cells in many cases )
are reduced to only a few cells ( just three cells in many cases )