Abstract
In the swelling piller-shape part of rachilla vascular bundle of rice spikelet, ramificated xylem, phloem and unlignified thick-walled parenchyma cells elabolate a mosaic structure (Fig. 1 and 2). There can be observed no transfer cell, but sieve elements are surrounded with a number of large phloem parenchyma cells including abundant mitochondria (Fig. 1, 2 and 6), and the thick-walled parenchyma cells are rich in simple pits and smooth endoplasmic reticulum (Fig. 3 and 6) connecting with cortical sclerenchyma cells (Fig. 2). For about 25 days after flowering, starch grains are observed only in the cortical sclerenchyma cells and the thick-walled parenchyma cells of rachilla bundle (Fig. 6), and subsquently disapear. By tracing barium chloride absorbed through the roots, no transpiration stream can be observed in the piller-shape part of the rachilla bundle. It is supposed, that the phloem parenchyma cells provide the sieve elements with the energy necessary for phloem active transport, that the turgor pressure of the sieve elements is controlled by putting in and out the water and solutes of sieve elements, and that the tracheids function as drainpipes of water.
