Apical organisation and vascular differentiation inMicrolepia in relation to stelar architecture
The growing apex of the rhizome ofMicrolepia speluncae has a tetrahedral apical cell crowning a pad of meristematic cells located on the dorsal surface behind a semicircular dorsiventral leading ledge at the tip. Leaf initials are formed anterior to the apical cell and the youngest 2 or 3 leaves are anterior to the meristem. Each leaf initial is associated with 4 primary roots two of which are anterior and two posterior to the apical cell; root initials are superficial at origin. Provascular tissue is formed associated with leaves and roots only. Leaf trace is channel-shaped and gets connected to vasculature of the primary roots, which in turn gets connected secondarily to the vasculature of the next older leaf; young region of rhizome, thus, has a channel-like stele open ventrally but the margins get connected later by secondary provascular tissue formed from intervening parenchyma. Leaf traces and stele of younger regions are highly dissected; the parenchyma in the perforations, transforms into provascular tissue as the rhizome matures, rendering leaf traces and stele intact. The rhizome branches after every 3rd leaf; branch initial is an apical cell formed away from the apical cell of the rhizome. Vasculature of branch is associated with the leaves produced by the branch apex and gets connected to the main stele on its dorsal side. The rhizome is interpreted as a fusion product of leaf bases.
KeywordsApical organisation vascular differentiation Microlepia stelar architecture
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