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January, 2020

  • 12 January

    Pteridophytes: Origin and Evolution

    They are the earliest known vascular plants that originated in the Silurian period (400 million years ago) of the Palaeozoic Era and subsequently diversified and formed the dominant vegetation on earth during Devonian to Permian period. There are controversies regard­ing their origin and evolution. There are two broad theories about …

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  • 12 January

    Evolution of Plants: Telome Theory

    Telome theory was proposed by Walter Zimmerman (1952, 1965). This theory is based on fossil records and explains the major steps in the evolution of vascular plants. According to this theory, all vascular plants have evolved from simple, leaf-less, root-less and dichotomously branched sterile and fertile axes called telomes which …

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  • 11 January

    Identification Of Ascomycetes: The Sac Fungi

    In the kingdom Fungi, there are two major phyla- Ascomycota and Basidiomycota. These two together form a subkingdom of fungi named as Dikarya. They together were named such as members of both phyla maintain most part of their life cycle in dikaryotic stage meaning each cell contains two genetically different …

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  • 11 January

    Experimental Embryology: Bringing Embryology Under Human Control

    Modern embryology seems to comprise three main disciplines. The first, or descriptive embryology, is a study of the various developmental processes that take place in a plant from the initiation of the sex organs to the maturation of the embryo. The second, or phylogenetic embryology, attempts to evaluate these data …

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  • 10 January

    Polyembryony: Multiple Embryos in a Seed

    The phenomenon of polyembryony, i.e., the occurrence of more than one embryo in a seed, has attracted much attention ever since its initial discovery in the orange (Citrus sinensis) by Leeuwenhoek (1719). Ernst (1918) and Schnarf (1929), who have reviewed the older literature, classify it into two types—”true” and “false”—depending …

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  • 10 January

    Apomixis: A Subistitution for Sexual Reproduction

    Apomixis maybe defined (Winkler, 1908, 1934) as the substitution for sexual reproduction (amphimixis) of an asexual process which does not involve any nuclear fusion. For the sake of convenience it may be subdivided into four classes. Non-recurrent apomixis Recurrent apomixis Adventive embryony Vegetative propagation Non-recurrent apomixis In the first, or …

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  • 7 January

    Steps of Fertilization

    Fertilization is the union of male and female gametes to produce a zygote. There are several steps of fertilization. They are described below. Germination of Pollen. The course of the pollen tube. Entry of pollen tube into the ovule. Entry of pollen tube into the embryo sac. Gametic fusion. Germination …

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  • 7 January

    Female Gametophyte: The Embryo Sac with Its Types

    The angiosperm female gametophyte is critical for plant reproduction. It contains the egg cell and central cell that become fertilized and gives rise to the embryo and endosperm of the seed, respectively. Female gametophyte development begins early in ovule development with the formation of a diploid megaspore mother cell that …

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  • 7 January

    Nemec Phenomenon: Embryo Sac Like Pollen Grain

    In 1898, Nemec noted that in the petaloid anthers of Hyacinthus orientalis, the pollen grains sometimes form large eight-nucleate structures showing a surprising resemblance to embryo sacs. He believed that they arose as the result of a degeneration of the generative nucleus and three divisions of the vegetative nucleus of …

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  • 7 January

    Discovery about the Male, Female Gametophytes & Syngamy

    Among early students of the development of pollen, Hofmeister (1848) presented some surprisingly good illustrations of the process of tetrad formation (microspore tetrad), and Reichenbach, Hartig and several other workers noted the presence of two nuclei in whole mounts of the mature pollen grains of several angiosperms. Discovery of nature …

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