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Calcium-containing crystals have been found in the lumens of secondary tracheids in the rhizome of the woody fern Botrychium multifidum. These crystals are styloids with rough, pyramid-shaped ends. The crystals are usually single; however, conjoined or grouped crystals were also found. Crystal formation apparently has no constant relation to the pit membrane, but crystals of mature tracheids are often associated with the pit membrane or are located in the pit areas. Crystals were also located between the helical thickenings of the lumen walls. No crystal chamber or crystal sheath was found in association with the crystal body.
In their natural environments pteridophytes usually have regular sporing periods, the onset of which is triggered by the interaction of climatic and nutritional factors. Little, however, is known about what changes there may be in the sporing behaviour of a fern when it is transferred from its natural habitat to an artificial environment, such as a glasshouse. We recorded sporing behaviour in relation to vegetative growth in two genetically matched populations of Polypodium vulgare. One population was placed in a controlled-climate glasshouse, the other was left outside. The recruitment of new fronds was significantly higher in the indoor population than in the outdoor population. The indoor population also maintained a high proportion of actively sporing fronds throughout the winter. There was no net recruitment of new fronds in the outdoor population during the winter and early spring. Some elements of the glasshouse environment, probably the enhanced light and temperature, induced continuous sporing in this fern. Considering the ever-increasing interest in ferns as ornamental plants, and the growing body of evidence of toxic and allergenic effects caused by fern spores, this kind of sporing behaviour may have implications for human health.