| 英文摘要 |
The anatomical and histological studies were made on the developing roots of more than ten species of orchids from Taiwan. The present investigation has revealed that with the exception of the apical organization, the various tissues in all the roots show very similar patterns. In which, as is seen in transverse sections from the periphery of the root centripetally, they can regularly be divided into the following tissues: a one to several layered, dead celled velamen; a uniseriate thick walled exodermis with short and long cells which are interposed with each other; a multiseriate parenchymatous cortex proper; a one cell layered, thick-walled endodermis which is interrupted by the thin-walled cells (endodermal passage cells) at the regions opposite to every protoxylem pole; a central stele with several groups of xylem and the same number of groups of phloem peripherally arranged surrounding the sclerified pith. The variation of some tissues, especially the velamen, are here discussed based on phylogeny as well as on environmental conditions. The uniseriate velamen more strongly retains the nature of a normal epidermis than does the multiseriate ones. The multiseriate velamen may have lost its original function of absorption during its phylogenetic advancement. |
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