The Growth of Protonema Cells and Rhizoids in Bracken

Abstract

The elongation of protonema cells and rhizoids of bracken was studied by the direct measurement of shift of marks made on the wall surface with a micromanipulator. The apical cell of the protonema elongates chiefly in its apical dome, very slightly in the region more than 10 u from the apical end, and not at all in the region over 30u from the apical end. Some of the subapical cells elongate and make tip growth, but their elongation is less than that of the apical cell. The 3d cell, less often than the subapical cell, grows slightly at its apical end. The 4th cell does not elongate. There exists a polarity from apex to base, so that the nearer to the apex the given part is, the greater the possibility and ability it has to elongate. Rhizoids elongate in that portion within 1u or less of their tip.