Ultrastructure of unique plasmodesmata in Selaginella willdenowii.

All meristematic cells of dorsal angle meristems of Selaginella willdenowii Baker cultured in vitro possessed expanded plasmodesmata, unlike the conventional plasmodesmata which were also found in these cells. Apical tissues of stems, roots and shoots from intact plant also possessed these structures though to a lesser degree than angle meristems. Root tips and stem apices had numerous conventional plasmodesmata in their walls. The expanded plasmodesmata, with their marked symmetry, represent a unique variation of plasmodesmatal structure.