Gametophyte and Sex Organs of Reboulia hemisphaerica

Abstract

1. Reboulia comprises a single polymorphic species, R. hemisphaerica, belonging to the Operculatae division of the subfamily Marchantioideae. 2. The thallus bears smooth and pegged rhizoids and 2-ranked ventral scales without appendages. The body is differentiated into a dorsal and ventral region, and grows by means of a single cuneate apical cell. 3. Air chambers are abundantly formed and develop by centripetal splittings. Secondary partitions separate the primary air chambers. No chlorophyllose filaments are formed. 4. Barrel-shaped air pores are developed on the female receptacle. Those of the thallus and male receptacle are made up of a single layer of concentric cells. 5. Reboulia is monoecious (autoicous). The antheridial receptacle is sessile, and several may be produced during the growing season, but the formation of the archegonial receptacle terminates apical growth of the thallus and represents a definite branch system, as among the higher members of the order. 6. The antheridia develop like those of the other Marchantiales. 7. In the development of the archegonium the 3 vertical walls follow the appearance of a transverse wall in the initial cell, and further development is typical. Eighteen to 20 neck canal cells are formed, but only 4 are present at the time of division of the ventral cell. 8. Several growing points are organized in the female receptacle from segments of the apical cell of the thallus, and each new apical cell comes to lie in a receptacle notch. Only 1 (rarely 2) archegonium is formed from the immediate segment of each apical cell.