Abstract

The growth of prothallia of Ceratopteris thalictroides in area was seriously restricted under the full intensity of sun light in the greenhouse. By shading, however, the growth was improved. In the early period of their growth, the growth was better under l/8-1/4 sun light. As the prothallia g'rew older, the better growth was made under l/2 sun light. It is thought that these results are related to the 'smallness' of the prothallium; the prothallium has to be smail in order to get a suitable shading with ease in a small hollow of the ground. The best growth was made when the prothallia were placed in continuous dayjight fluorescent light in culture room. All conceptrations of gibbereljic acid (GA) ranging from 0.01 to 100 ppm inhibitedthe growth of prothallia during the early stage of their growth under all intensitied sof sun light. As the prothallia grew older, the Iower concentrations (e.g., 0.01 ppm)became effective to promcte the growth of prothallia which showed less growth under weak sun light. It thus appears tbat the lower concentrations of GA are effective to reverse the growth limitation imposed by the lower intensities cf sun light. The effect of GA and light conditions on sexuality was indirect; primarily, GA and light conditions affected greataly on growth. More sex organs were formed on those prothallia which showed better growth in area. Both unisexual and bisexual prothallia were obtained in the present study. It is suggested that a Iarge heterogeneity sexuality in this fern is presumably related to antheridium-inducing substances. The larger prothallia with antheridia less than five were always found forming the sporophyte. On rare occasions, two sporophytes were developed from two different archegonia on the same prothallium.