Fig. 1. Rhizoid development in the wild type. (A) A juvenile and (B) an adult leaf. (C) A juvenile gametophore with the first rhizoid (arrow). (D) An adult gametophore with 17 leaves. Lines G, K, L and M indicate transverse sections in G, K, L and M. The white and black arrows indicate the uppermost mid-stem rhizoid and the uppermost juvenile leaf, respectively. (E) A mid-stem rhizoid formed below an adult leaf. (F) The midrib cells (pink) and a mid-stem rhizoid (green). (G-M) Transverse sections of a gametophore with 18 leaves. The asterisk in G indicates the abaxial epidermal cell of a midrib in the same longitudinal cell file as the uppermost mid-stem rhizoid. (H) A line drawing of G showing hydroids in the center of the stem (red), leaf traces (green) and a midrib (blue). (I) A higher magnification of the midrib. (J) A line drawing of I showing epidermal cells (light blue), stereids (yellow), hydroids (pink) and deuters (orange). The asterisk in K indicates the uppermost mid-stem rhizoid. The single and double asterisks in L indicate the first and the second mid-stem rhizoid, respectively. The arrows in K and L indicate leaf trace cells. Scale bars: 100 µm for A,F,G,K-M; 250 µm for B,E; 50 µm for C; 1 mm for D; 20 µm for I.