• S Sundara Rajan

      Articles written in Proceedings – Section B

    • Embryological studies in compositae - III. A contribution to the embryology ofBlainvillea rhomboidea, Cass. (B. latifolia, DC)

      S Sundara Rajan

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      InBlainvillea rhomboidea, Cass. the floral parts arise in acropetalous succession. The archesporium consists of two linear rows. of cells In the fully formed anther there is an epidermis, an endothecium, a middle layer, a tapetum and two linear rows of microspore mother cells. Tapetal cells become binucleate and are of the plasmodial type. Microspore tetrads are isobilateral, tetrahedral and decussate. Exine of the pollen grain is echinate. Shedding is at the three-celled stage as in the majority of Compositae. Endothecium shows faint fibrillar thickenings at the time of anther dehiscence.

      Ovules are anatropus, unitegmic and tenuinucellate. A hypodermal archesporial cell directly functions as the megaspore mother cell. Embryo sac development is of the Polygonum type. More than one megaspore in the tetrad show signs of development. Organised embryo sac is six-celled with only two antipodals. A secondary multiplication of nuclei in the antipodal cells results in a variable number of nuclei.

      Endosperm is of theab initio cellular type.

      Embryogeny conforms to Asterad type.

      Fruit wall has a thick layer of tannin cells in the hypodermal layers.

    • A contribution to the embryology ofOldenlandia umbellata Linn.

      G Shivaramaiah S Sundara Rajan

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      The embryology ofOldenlandia umbellata Linn. has been investigated. Floral parts arise in acropetalous succession. A transection of an young anther shows a group of microscope mother cells followed by a layer of tapetum, a middle layer, an endothecium and an epidermis. The uninucleate tapetum is of the glandular type. Microspore tetrads are tetrahedral and isobilateral. The pollen grain is binucleate at the time of anther dehiscence and the endothecium fibrillar. A hypodermal archesporial cell directly functions as the megaspore mother cell. Embryo sac development follows the Polygonum type. Fertilisation is porogamous. Endosperm is free nuclear and embryogeny conforms to the solanad type.

    • Embryological studies in compositae - IV. A contribution to the life-history ofSpilanthes acmilla, Murr. (S. calva, Wt. Ic.)

      S Sundara Rajan

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      Morphology and embryology ofSpilanthes acmilla, Murr. has been investigated and its systematic position in the tribe Heliantheae is discussed. Floral parts arise in acropetalous succession. Stamens are four to five in number with bisporangiate anthers. Tapetum is of the plasmodial type. Pollen grains have an echinate exine and are shed at the three celled stage. Endothecium exhibits fibrillar thickenings at the time of anther dehiscence. Ovules are anatropous, unitegmic and tenuinucellate. Embryosac development conforms to the Polygonum type. In a great majority of cases organised embryosac is six celled with only two antipodals. Occasionally the number of antipodals may be three or four. There is a great variety in the nuclear behaviour in the micropylar antipodal in having a secondary multiplication and subsequent fusion resulting in the formation of a polyploid nucleus. Very rarely aposporic uninucleate embryosac-like structures are noticed at the chalazal end of the ovule. These however do not show any influence on the sexual behaviour of the gametophytes.

      Fertilisation is porogamous, endosperm isab initio cellular and embryogeny conforms to thesenecio variation of the Asterad type.

      In the mature fruit, the wall is five layered with the innermost layer infested with tannin. Endosperm persists as a thin layer adhering to the integument which itself is three layered.

    • Embryological studies in lentibulariaceae - I. Floral morphology and embryology ofUtricularia smithiana, Wt. Ic.

      S Sundara Rajan D Jeevan Kumar

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      Embryology ofUtricularia smithiana has been studied and its systematic position as a species separate fromUtricularia caerulea has been justified.

      Floral parts arise in acropetalous succession. A transection of an young anther lobe shows a layer of microspore mother cells surrounded by tapetum, a middle layer, an endothecium and an epidermis. Microspore tetrads are decussate and tetrahedral. Tapetum is glandular. Pollen grain is shed at the 3-nucleate stage. Endothecium exhibits fibrillar thickenings.

      Embryosac development is of the polygonum type. Placental nutritive tissue is present only at the micropylar region. Embryosac is surrounded by the endothelium only at the central region.

      Fertilisation is porogamous and endosperm isab initio cellular. Endosperm haustoria are not very aggressive. Embryogeny conforms to solanad type. Mature embryo is undifferentiated with starch grain filled cells.

    • Micropyle formation in the ovule as an indicator of primitiveness in Angiosperms

      S Sundara Rajan

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      It has been shown by statistical methods that in Angiosperms significant correlation exists between micropyle formation by both the integuments and six other floral and vegetative characters which are admittedly primitive. A subjective assessment of the primitiveness of the feature in question (i.e., micropyle formation by both the integuments) supports the statistical findings.

    • Reverse polarity inNauclea orientalis, L. (Sarcocephalus cordatus, Miq.)

      S Sundara Rajan G Shivaramaiah N Sathyananda

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      Embryo sac development conforms to Polygonum type. Starch grains are noticed in the embryo sac right from the megaspore mother cell stage. Twin tetrads one with a chalazal functional megaspore and another with a micropylar functional megaspore have been noticed in some ovules. While 75% of the embryo sacs have normal polarity, in 20% of the ovules reverse polarity has been noticed. In the remaining 5% of the ovules, ‘bipolarity’ has been observed. Reverse polarity in relation to double archegoniate theory has been discussed.

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