Resumen:
The development of Desmarestia antarctica has been studied under seasonally daylenghts mimicking the daylength conditions on King George Island (Antarctica). Under June conditions the sporophytes were uniseriate. Primary laterals developed in July, secondary laterals were observed in September. Cortication of the main axis and primary laterals started in October and November, respectively. Shedding of uncorticated parts was observed in the entire growth period of the sporophyte. In February all uncorticated filaments were shed. The main axis of October - November developmental stages consists of several layers of small outer cortical cells, larger inner cortical cells, into which smaller cells are interspersed, and the axial cell row. Around the axial cells a trasitory pericentral caviry is developed, which is filled in the later stages by small cells forming a sheath. Cells of the axial filament show the characteristics of trumpet cells, which imply a tansport function. Occlusions of their lumen apparent in sections of chemically fixed cells are artefacts since they were not found in clyofixed plants. X-ray microanalyses revealed considerably higher concentrations of K+ and CL- in cortical compared to axial cells, pointing to the presence of organic translocates in the axial cells. The vegetative structure of the gametophytes varies depending ont he light conditions. Gametogenesis was observed al temperatures < 5ºC