● The gymnosperms are heterosporous; they produce haploid microspores and megaspores.
●The two kinds of spores are produced within sporangia that are borne on sporophylls( microsporophyll and megasporophyll) which are arranged spirally along an axis to form lax or compact strobili or cones.
● The strobili bearing microsporophylls and microsporangia are called microsporangiate or male strobili.
● The microspores develop into a male gametophytic generation which is highly reduced and is confined to only a limited number of cells.
● This reduced gametophyte is called a pollen grain.
●The development of pollen grains takes place within the microsporangia.
● The cones bearing megasporophylls with ovules or megasporangia are called macrosporangiate or female strobili.
●The megaspore mother cell is differentiated from one of the cells of the nucellus.
●The nucellus is protected by envelopes and the composite structure is called an ovule.
● The ovules are borne on megasporophylls which may be clustered to form the female cones.
● The megaspore mother cell divides meiotically to form four megaspores.
●One of the megaspores enclosed within the megasporangium (nucellus) develops into a multicellular female
gametophyte that bears two or more archegonia or female sex organs.
●The multicellular female gametophyte is also retained within megasporangium.
●The male or female cones or strobili may be borne on the same tree (𝘗𝘪𝘯𝘶𝘴) or on different trees (𝘊𝘺𝘤𝘢𝘴).