(i) Protonema: The predominant stage of the life cycle of a moss is the gametophyte which consists of two stages. The first stage is the protonema stage, which develops directly from a spore. It is a creeping, green, branched and frequently filamentous stage. The second stage is the leafy stage, which develops from the secondary protonema as a lateral bud.
(ii) Antheridium: Anthers are present in bryophyte and pteridophyte plants. Anther is the male genital organ and is multicellular. From these, haploid spermatids are produced. These are dicotyledons and by swimming in water they reach the archegonium and take part in the fertilisation process.
(iii) Archegonium: These are female sexual reproductive organs which are found in bryophyte, pteridophyte and gymnosperm plants. These are flask shaped and multicellular. There is a haploid egg in its basal swollen part. The egg fuses with the sperm to form a diploid zygote.
Example: Riccia.
(iv) Diplontic: In gymnosperm and angiosperm plants the main body is diploid i.e. sporophyte. The sporophyte is dominant, photosynthetic and free. In these, haploid male and female gametes are formed due to meiosis during gamete reproduction process. Gametophytes are haploid and unicellular or few cellular. Fusion of gametes again results in the formation of sporophyte. That is, the sporophyte is dominant and the part of the gametophyte is transient. This stage of the life cycle is called diploid. Diploid state is found in all seed plants.
(v) Sporophylls: In pteridophyte plants, the leaves on which sporangia grow are called sporophylls. In some pteridophytes, the sporophylls condense and form a distinct structure called a cone. Example: Selaginella, Equisetum. Spores located in the sporangia become spores due to meiosis in the mother cell. The spores germinate and form a haploid prothallus.
(vi) Isogamy: This stage is found in the reproductive process of algae. When both the gametes fusing in an alga are of the same type, it is called isogamy sexual reproduction.