Angiosperm

Polyembryony: Multiple Embryos in a Seed

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

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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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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. Course of pollen tube. Entry of pollen tube into ovule. Entry of pollen tube into embryo sac. Gametic fusion. Germination of pollen Exact information …

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Female Gametophyte: The Embryo Sac with Its Types

Depending on the number of megaspore nuclei taking part in the development, the female gametophytes of angiosperms may be classified into three main types: monosporic, bisporic, and tetrasporic. In the first, only one of the four megaspores takes part in the development of the gametophyte. In the second, two megaspore …

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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. De …

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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, 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 of pollen …

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Pollen Tube Discovery by G. B. Amici

Giovanni Battista Amici (1824) who was also a good microscope maker, found that the stigma of Portulaca oleracea was covered with hairs which contained some granules or particles inside them. Curiosity prompted him to ascertain whether they moved in the same way as the granules he had seen in the …

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Chemotaxonomy: Semantides

Semantides are information-carrying molecules. Semantides provide taxonomic data not on the basis of presence or absence, but in terms of sequences, ratios or percentages,. Semantides are of three types, viz., Primary semantide – DNA Secondary semantide- RNA Tertiary semantides – Proteins Sometimes the semantides together with the larger polysachharides, are …

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Chemotaxonomy: Secondary Metabolites

The chemical substances which have been found very useful in taxonomy are secondary metabolites. Secondary metabolites (secondary plant products) perform non-vital (or at least non- universally vital) functions, and are less widespread in plants. The restricted occurrence of these metabolites among plants renders them valuable as taxonomic information. Secondary plant …

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