莲的根茎构造,伸长与增粗

莲 (Nelumbo nucifera)种苗的茎短而直立,叶互生。幼苗期茎延伸成横卧根茎,其上生有营养芽及混合芽。腋生鳞片为叶的衍生部分,形如叶鞘状,包着预芽。年苗上的冬芽内全为混合芽。根茎内的维管束分散排列,无导管及形成层存在。节间延长通过肋状分生组织及节间内的薄壁组织细胞分裂与增长来完成。根茎可由初生加厚分生组织,维管束细胞,皮层薄壁细胞等的细胞分裂,使层次增加,但增粗主要是由皮层薄壁细胞体积显著增大而引起的。

THE STRUCTURE,ELONGATION AND THICKENING OF RHIZOME IN IVELUMBO NUCIFERA GAERTN

The seedling of Nelurnbo nucifera is erect and its internodes are very short with four Alter- nately arranged floating leaves.During the juvenile stage,the shoot elongates remarkably and forms the horizontal rhizome.Each leaf grows out from the dorsal side of the node of the rhizome. There are two kinds of terminal buds in the juvenile shoot.(1)vegetative bud and(2) mixed bud.The axillary scale is the derivative part of the leaf.It forms an ochrea around the terminal bud.The winter buds on the annual shoot are all mixed buds.The vessels are absent in the rhizome and no cambium exists. During the early growth of the rhizome,the rib meristems contribute mainly to the in- ternode elongation.Later however,divisions are seen to commence in the parenchymatous tissue of the internode.As a result of these divisions the internode becomes elongated. The tuberization of the rhizome is built up from cell divisions of three kinds of tissues: (1)primary thickening meristems,(2)cells of the vascular bundles and(3)parenchyma of cortex.But,the growth in thickness of the rhizome seems to be chiefly due to the enlargement of parenchymatous cells.