C4植物之所以比C3植物光合效率高在其形态学来讲是因为它的维管束鞘薄壁细胞不但大而且里面有叶绿体，虽然是未发育完全的叶绿体，而C3植物维管束鞘细胞不但小而且也没有叶绿体。
显微镜观察表明在烟草发根的维管束中柱鞘细胞、水稻根皮层细胞内和细胞间隙有根瘤菌存在。
The observation under microscope showed that the rhizobia were present in percycle cells of vascular system of the tobacco hairy roots and in cortex cells and intercellular spaces of rice roots.
维管束由维管束鞘、木质部、韧皮部和大型薄壁细胞组成。
The vascular bundle consists of vascular bundle sheath, xylem, phloem and big parenchymatous cells.
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