Differentiation of Sporangia in Marsilia quadrifolia

Abstract

1. The microsporangia and megasporangia of Marsilia are derived from sister cells. 2. The stalk of the microsporangium is very much longer than that of the megasporangium. 3. In the spore mother cell stage the microsporangia are elongated and oval, while the megasporangia are somewhat flattened. 4. The sporangia differ in their time of development. In the megasporangium there is a gradual continued development of the sporogenous tissue; in the microsporangia there is delay in the development of the sporogenous tissue, while the apical cell cuts off segments to form an elongated stalk. 5. The megaspore mother cell in diakinesis shows a pair of large chromosomes which may be sex chromosomes. 6. Since Marsilia is a monoecious plant, sex differentiation must have occurred in some somatic mitosis. 7. When the single functioning megaspore has gained ascendency, the sporogenous tissue of the microsporangia resumes growth and develops very rapidly. 8. The protoplasmic strands between the tetrads of megaspores are much stronger and more persistent than in the microspores. 9. The functioning megaspore is surrounded by a mass of vacuolated cytoplasm, in which the tapetal nuclei as well as the aborted spores may be found. 10. In each of the six genera of heterosporous Pteridophytes the difference in the sporangia becomes visible at a different stage. If the chromosomes were examined it would probably be found that the differentiation of sex had occurred in an earlier somatic cell.