Floral morphology of the family compositae
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Vernonia anthelmintica (Linn.) Willd., tribe Vernonieae, family Compositae has been studied. The cypsela has dimorphic pappus, 20 longitudinal ribs (10 primary and 10 secondary), and two types of hairs developing from single epidermal cells on surface. Certain features of vasculature of floret observed in this taxon have been considered as intermediate between relatively primitive and highly advanced conditions known in the family. Others elucidate further that the ovary is bilocular with axile placentation at base in which region the ovule is attached, and unilocular with parietal placentation in the remaining portion, and also that the ovule possibly belongs to one of the two carpels, which alone is fertile, and is an organ morphologically double in nature. The pappus has been regarded as a longitudinally dismembered calyx tube.
The tissue of the ovule outside nucellus differentiates into an endothelium, a periendothelial zone, and an outer zone. In the mature seed the thickned outer epidermis and remmants of a few subjacent layers form the outer zone, and endothelium redued to a pellicle, the inner zone of the seed coat. The jacket layer of the endosperm persists between the seed coat and the dicotyledonous, orthorrhizal embryo.
The pericarp development resembles that of most other Compositae in an early differentiation of the ovary wall into two zones, and later breakdown of a major part of the inner zone. But it is quite characteristic in other respects, especially, the peripheral chin of firovascular bundles which forms its main mechanical zone.
KeywordsSeed Coat Outer Zone Sieve Tube Floral Morphology Megaspore Mother Cell
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