Extended Data Fig. 3: Fundamental tissues present in an apex of a rooting axis preserved after growth had finished, and a meristem of a rooting axis preserved during active growth.
From: Stepwise and independent origins of roots among land plants
a, b, Root apices with fundamental tissue types colour-coded. Blue, epidermis; pink, promeristem; orange, cortex; and green, procambium. c, d, Magnified images of the apical regions of a (c) and b (d). The presence of differentiated vascular tissue (arrowhead, c) close to the tip of the apex indicates that this apex was not active at the time of preservation. By contrast, in d there is no differentiated vascular tissue. Instead, the apex is characterized by large numbers of cells and cell size gradually increases with distance from the tip, which indicates that the apex was active when fossilized. a, c NHMUK V.15642 (same specimen as illustrated in Fig. 1a), b, c, OXF 108 (same specimen as illustrated in Figs. 1d, 2a, b). Scale bars, 500 μm (a), 250 μm (b), 150 μm (c), 100 μm (d).
