COMPARISON OF SPOROPHYTE OF BRYOPHYTES

            The sporophytes of bryophytes start from simplest organization of structure to the highest complex structure of different genus of bryophytes. The complexity is due to the progressive sterilization of the potentiality of fertile cells (Bower), which results in the formation of different types of sterile tissue system in the sporophyte. The simplest structure of sporophyte is seen in genus Riccia in which almost all the sporogenous cells are fertile and proceeds to the highest complex form of sporophyte found in the genus Funaria in which only a single layer of cells is fertile and most are sterile to form the complex structure.

            The detailed comparisons of complexity of the sporophytes of bryophytes are as follows –

            (a) Riccia Sporophyte. In Riccia, the zygote divides and redivides to form a mass of spherical mass of 20-30 undifferentiated cells. Periclinal segmentation forms an inner mass of cells called endothecium and outer single layer amphithecium. The amphithecium forms the single layered capsule wall. The endothecium forms the central mass of sporogenous tissue. Practically, all the sporogenous cells are fertile and develop into spores. However, few of them undergo degeneration to form the nurse cells.

            The sporophyte of Riccia is the simplest among all the bryophytes and has the least amount of sterile cells. The entire embryo forms the spore producing capsule. There is no foot and seta. It is just a spore producing organ without any distributing function.

            (b) Marchantia Sporophyte. Sterilization of the fertile cells is more advanced in this genus. Half of the embryo derived from the hypobasal region remains sterile. It forms the foot and the seta. The upper epibasal half is fertile and forms the spore producing capsule. The sterile cells elongate, develop spirally thickened walls and become the elaters. A few of the cells of sporogenous cells at the top may differentiate into sterile, apical cap.

            The capsule of Marchantia has both spore producing and spore distributing body. It illustrates a step further in the progressive sterilization of the sporogenous tissue.

            (c) Anthoceros Sporophyte. It illustrates a step further than Riccia and Marchantia in the progressive sterilization of the potentiality of fertile tissue. The endothecium cells become completely sterile and forms a group of cells known as columella. The sporogenous cells arise from the innermost layer of the amphithecium. It surrounds the columella. The sporogenous cells become differentiated into spore mother cells and pseudo-elaters. The archesporium of Anthoceros is extremely reduced. The outer amphithecium develops into several cells layer thick capsule wall. The capsule wall develops a well ventilated photosynthetic tissue protected by the epidermis.

            (d) Funaria Sporophyte. In Funaria, major portion of the sporophyte remains sterile to form the foot and the seta. The capsule is differentiated into central column of endothecium surrounded by many layered amphithecium. The inner layer of the endothecium forms the sterile columella and the superficial cells forms the sporogenous tissue. Thus the archesporium arises from the outermost layer of cells of the endothecium. It is thus extremely reduced and consists of single layer of fertile tissue. The amphithecium becomes differentiated into the epidermis, the photosynthetic tissue of the capsule wall and the outer spore sac.

            Thus from the above discussions, it is clear that the sporophytes of bryophytes become more and more complex in upward direction because of the gradual sterilization of the fertility of sporogenous tissue.

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