• K Periasamy

      Articles written in Proceedings – Plant Sciences

    • The aim and scope of plant morphology—II

      K Periasamy B G L Swamy

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      Evolution was in the beginning applied to the species. When genetics established the independent inheritance of characters, evolution also began to be analysed in terms of characters or organs, each considered independent in its evolutionary trend. Subsequently, however, this rule of independence began to be violated in the attempts to determine evolutionary status by correlation. Furthermore, the circumscription of an organ for evolutionary correlation is equivocal. With regard to the vegetative and floral morphology of the angiosperms, the concepts of old formal morphology in terms of fundamental organs were more definite and evolution has not been able to offer anything better. Many of the concepts of formal morphology havein toto been transferred to evolution.

      The principles laid down by Carlquist, in what he has proposed to be a function oriented approach to angiosperm morphology, appear to be based on undue assumptions with a mixing up of homology and evolution. The decline of evolution as the directive force behind plant morphology necessitates new approaches that could impart dynamism to this basic discipline of botanical study.

    • Ontogeny of palmately compound leaves in angiosperms: 1.Tabebuia pentaphylla Hense

      K Periasamy E A Muruganathan

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      The palmately compound leaf ofTabebuia pentaphylla is initiated by periclinal division in the hypodermal layer at the flank of the maximal shoot apex, which lacks cytohistological zonation. The growth of the leaf primordium is diffuse until it reaches a height of 50–60 μm after which an adaxial meristem makes it conspicuously thick at the basal region. The first pair of lateral leaflets arise about 50 μm below the tip of the leaf primordium when the latter is about 150 μm high and before the differentiation of a well defined marginal meristem. The second pair of leaflets arises subsequently below the first. The terminal portion becomes the central leaflet. The sites of leaflet initiation are the terminal endings of acropetally differentiating procambial strands. The 6-layered plate meristem of the leaflet lamina arises from a marginal meristem whose submarginal initial is wedge shaped. Leaflet venation is comptodromous and the ultimate areoles lack free vein endings.

    • Ontogeny of palmately compound leaves in angiosperms: 3.Arisaema Spp.

      K Periasamy E A Muruganathan

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      Arisaema is mono or bifoliar, exhibiting sympodial growth with annual conversion of the shoot apex into the floral apex. The shoot apex shows pendulum symmetry during successive plastochrons.

      Leaf initiation is hypodermal. The primordium quickly acquires the configuration of a 5 layered laminar plate meristem and its base extends around the shoot apex as the sheath. Following this, apical growth ceases in the primordium. Its apex becomes a hood like lamina wing and the sheath develops a median adaxial meristem which leads to its thickening. The lamina wing expends and becomes plicately folded at right angles to its surface. Each fold becomes a leaflet by the elongation of the abaxial edges and suppression of the adaxial edges of the folds. Early abortion of the lamina wing results in a scale leaf which comprises the sheath portion alone.

      An adult leaf has 300-400 veins which run independently from the corm to the leaflets through the petiole. The dorsal median strand develops first and goes to the midrib of the median leaflet. Subsequent strands arise laterally on either side of this in a series of tangential rows. Those of the first row bifurcate at the tip of the petiole to enter two neighbouring leaflets. The strands run parallel in the leaflet midrib and diverge at different levels into the lamina as lateral veins.

    • Anther development inXylopia nigricans

      K Periasamy S Thangavel

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      In the anther primordium ofXylopia nigricans, the archesporium differentiates discontinuously with intervening sterile tissue. Each archesporial cell divides periclinally and develops into a micro-sporangium with a single microspore mother cell. Thus the anther becomes multisporangiate. The tapetal cells are uninucleate. Cytokinesis of the microspore mother cell is by successive cell plate formation. The pollen development is traced and the significance of the development is discussed.


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