Fig. 7

Schematic diagrams showing the process of rhytidome formation in Cryptomeria japonica (in radial view). a Stage 0: all axial and ray parenchyma cells in the inner bark and innermost phelloderm contain nuclei and large amounts of starch grains. b Stage 1: a new periderm is formed from axial and ray parenchyma of the outer part of the inner bark. In the secondary phloem between the new periderm and previous periderm, sporadic disappearance of nuclei and decrease in the amounts of starch grains are observed in axial and ray parenchyma cells. c Stage 2: new phelloderm and phellem are producing, indicating the development of a new periderm. In the outer region of the new periderm, many axial parenchyma cells have no nuclei. The amount of starch grains decreases across the entire inner bark and new rhytidome, particularly in the parenchyma cells outside the new periderm. d Stage 3: the secondary phloem outside the new periderm become indistinguishable from the rhytidome with brown cell walls, no nuclei and no starch grains. AP axial parenchyma cell, F phloem fiber, IB inner bark, N nucleus, NPr new periderm, NRh new rhytidome, Pr periderm, Pd phelloderm, Pg phellogen, Ph phellem, Rh (OB) rhytidome (outer bark), RP ray parenchyma cell, S sieve cell, St starch grain