Figure 1.

Cell divisions of gametophore apical stem cells. Optical transverse sections (i) and longitudinal sections (ii, iii, and iv) of gametophore tips cultivated under the regular growth conditions, producing leaf apical stem cells. Longitudinal section planes corresponding to (ii), (iii) and (iv) are indicated in (i) as dashed lines. (a) Developmental stage with the gametophore apical stem cell (*) and an immediate sister cell (†). (b) Developmental stage at which the immediate sister cell has divided to form a proximal cell (§) and a distal cell (#). The distal cell divides to form the leaf apical stem cell and the precursor cell for stem epidermis (‡). The leaf apical stem cell divides to form the self-renewed leaf apical stem cell (∞) and a leaf cell (¶). The fine lines in the drawings indicate cell division planes. All cells derived from each of the precursor cells descended from the gametophore apical stem cell are indicated by the same colour. Pale blue, yellow, green and purple cells are in order of the old derivative from the gametophore apical stem cell in pink. Scale bars, 20 µm.