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A first report on pulvinar wrist-joint and foliar nyctinasty in Malachra capitata (L). L. (Malvaceae)
BISWARUPA GHOSH
Abstract:
Leaf closing and opening movements were observed in Malachra capitata (Malvaceae) that followed a diurnal circadian rhythm in Sundarbans, West Bengal. However, the presence of pulvinus that is a prerequisite for such movement was not conspicuous morphologically on the dorsal surface of the leaf petiole. A paired T test at p=0.05 evinced significant difference in the collar diameter of the petiole base and its distal end on the ventral surface. The anatomical study of the petiole exhibited an eustele or dissected siphonostele. The collateral vascular bundles of the petiole were arranged in a single ring that was interrupted at several places with leaf gaps. On the other hand, the transverse section of the distal end of the petiole that appeared as an asymmetric swollen mass at the base of the leaf lamina exhibited an ectophloic siphonostele. The ectophloic siphonostele had a concentric ring of outer phloem facing the epidermis, inner xylem facing the central pith like collenchymatous parenchyma and a broad parenchymatous cortex surrounding the entire solid stele. This distal-end of the petiole or pulvinus facilitated a wrist- joint movement for leaf closing or upward vertical movement in the evening and leaf opening or horizontal movement in the morning. This is the first report of pulvinus at the distal end of the petiole that mediates night sleep or foliar nyctinasty in M. capitata.
Keywords: ectophloic, eustele, distal, petiole, pulvinus, siphonostele, solid stele.
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