Embryology of Sewardiella tuberifera Kash.

Abstract

1. The saddle-shaped vegetative body of Sewardiella tuberifera consists of a thick central midrib and two lateral thin flattened wings. Often the thallus is dichotomously branched. 2. The older ventral region of the midrib is profusely infected by an unseptate fungal mycelium which is probably in symbiotic relationship with its host. The fungus forms thick-walled vesicles which often fill the entire cavity of the infected cell. 3. The apical cell is tetrahedral with three cutting surfaces. 4. Perennation is accomplished by means of apical tubers. 5. The plants are strictly dioecious. 6. The antheridia are scattered on the dorsal surface of the midrib, each growing in the axil of a bract, though occasionally several may be present in the axil of a larger bract. They develop from the segments close to the apical cell and thus are strictly acropetal. Development is of the type usual in the Jungermanniales. 7. Archegonia of mixed ages are aggregated on the dorsal surface of the midrib into a cluster which is surrounded by bracts. Development follows the usual pattern in the Jungermanniales. The neck is composed of five to eight rows of cells, and as many as nine neck canal cells have been observed. The venter remains a single cell layer thick until fertilization. 8. The bell-shaped perianth develops by zonal growth at the base. The involucral bracts are carried up by this growth and not only form the lacerated margin of the cup but also occur on the inner and outer surfaces of the cup. Thus the perianth is of a composite nature. 9. Mother cells of the spores and elaters belong to the same cell generation. The protoplast of the spore mother cell is four-lobed, and tetrad formation following meiosis results from the deepening of the invaginations. 10. The bulbous foot is of Douin's generalized type, and its basal cells are haustorial in function. The capsule wall has three to four layers of cells, all of which show bands of thickening on the radial and inner walls. The spores are reticulate lamellate, and the small elaters are bi- or trispiral. 11. The haploid chromosome number is nine; the diploid, eighteen.