In rice plants, large traces of the panicle or each leaf run down through two internodes and turn into diffuse bundles in the second lower node (figs. l, 2 and 3). The diffuse bundles take oblique course surrounding the swelling elliptical leaf traces, and join with them only at the basal points of the node (○ mark in fig. 2). It may be supposed that assimilates from a leaf go down through the phloem of swelling leaf traces, and rise up through the diffuse bundles via the 〇 mark points by the metabolic activity of their numerous phloem parenchyma (figs. 7 and 10). In the xylem of swelling leaf traces, tracheids, and xylem parenchyma containing xylem transfer cells (figs. 17, 18, 19, 20, 21 and 22), display a mosaic structure (figs, 14, 16, 17 and 18). But, no phloem transfer cell has been found in the vegetative nodes. When the cell wall ingrowth of xylem transfer cells is formed in a vegetative node, the leaf of this node is developing out, and the second upper leaf primordium, about I mm long, begins to elongate, whose leaf traces do not function as conducting tissues yet. In the swelling leaf traces, solutes of transpiration stream are absorbed by the xylem parenchyma, and are raised to the upper internode by two pathways as follows. A part of the solutes moves horizontally into the phloem of the swelling leaf traces, and travels with assimilates. The other part moves horizontally across the bundle sheath and parenchyma bridges lying between the swelling leaf traces and the diffuse bundles (figs. 7, 23 and 24), and travels by the diffuse bundles. This supposition was able to be verified by the distribution in the node of barium absorbed the roots (fig. 25).
Crop Science Society of Japan