The Growth of Protonema Cells and Rhizoids in Bracken

The elongation of protonema cells and rhizoids of bracken was studied by the direct measurement of shift of marks which were made on wall surface with the micromanipulator. Those cells showed a typical tip growth. The apical cell of protonema elongates chiefly in its apical dome, very slightly in the region more than 10 microns from the apical end, and not at all in the region over 30 microns from the apical end. Some of the subapical cells elongate and make the tip growth, but their elongation is less than that of the apical cell. The third cell, less often than the subapical cell, grows slightly at its apical end. The fourth cell does not elongate. There exists the polarity, from apex to base, of the possibility and ability of elongation not only in each protonema cell but also in a protonema as a whole. The nearer to the apex the given part is, the larger the possibility and ability of elongation are, and vice versa. Rhizoids elongate at the part within 1 micron or less of their tip.