All bryophytes are oogamous. The spermatozoids (male gametes) are motile and small while the eggs (female gametes) are large and non motile.
The gametes (male and female) are produced within multicellular sex organs (antheridia and archegonia) in which there is an outer sterile layer of jacket cells. The antheridium (male organ) consists of a central mass of androcytes enclosed by a single layer of sterile jacket cells. Each androcyte metamorphoses into a biflagellate spermatozoid. The archegonium (female organ) is a multicellular flask-like structure. The basal swollen portion is venter and contains an egg (oosphere) in it. The elongated neck contains neck canal cells. Fertilization: The water is essential for the act of fertilization. The motile flagellate spermatozoid swims to the neck of archegonium and ultimately approaches the egg effecting the fertilization.
With the result the zygote (2n) is formed. The Sporophyte: The zygote divides repeatedly immediately after fertilization. There is no resting period. The first division of zygote is transverse and the embryo develops from the upper cell. Such emboryogeny is known as exoscopic embryogeny.
The embryo remains within the venter of the archegonium. The venter wall enlarges along with the developing embryo to form the protective envelope known as calyptra. Generally, the sporongonium consists of foot, seta and capsule. Here the sporogonium is completely dependent for its nourishment upon the gametophyte. The spore mother cells are developed in the sporogonium. They are diploid (2n) and represent the last stage of the sporophytic generation.
The spore mother cells (2n) undergo meiosis and the tetrads of haploid (n) spores are formed. All bryophytes are homosporous. The Young Gametophyte: The spores (n) represent the beginning of the gametophyte generation. The spores are cutinized and dispersed by means of wind. The spores may germinate directly into the new gametophyte (e.
g., in Riccia and Marchantia) while in mosses they germinate to produce filamentous protonema from which buds are produced to develop into new plants (young gametophytes).