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Information about Pollen Grains.
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The study of pollen grains is a branch of Paleobotany called Paylnology. Pollen grains are complex microscopic structures which contain the male genetic material of flowering plants. The release of pollen grains and their transfer to the female stigmas of flowers of the same species are essential phases in the reproduction of flowing plants. All the attractive characteristics of wild flowers (shape, colour and scent) are simply evolved adaptations to ensure successful pollination.Flowers producing highly sculptured and spiky pollen grains tend to be pollinated by insects. The bodies and appendages of insects are covered with numerous tiny hairs which inadvertently pick up pollen when the insect brushes against the anthers whilst probing the flower in search of nectar. This pollen may then be transferred to receptive stigmas when the insect visits other flowers.
Wind pollinated flowers (e.g., many trees, nettles and grasses etc) tend to be less conspicuous and usually produce vast quantities of pollen. It has been estimated that the Spruce forests of Southern and Central Sweden produce approximately 75 000 tons of pollen each year. An acre of ryegrass can produce approximately 80 kgm. of pollen in a single flowering season.
The surfaces of pollen grains contain specific chemical substances which enable the female stigmas to recognise the correct pollen and reject that of other species. It is these chemicals, rather than the external shape of the pollen grains, which trigger the release of histamines on contact with nasal tissue and that can initiate allergic responses in susceptible people (hay fever).
The shapes of pollen grains is determined by the means of dispersal employed by the plant and many wind pollinated plants and trees produce smooth pollen grains which are not very ornate. Other adaptations are used to increase the amount of pollen which can be dispersed. Pollen grains of rhododendrons, for example, are very similar in shape to those of heathers but are bound together with sticky viscin threads, which stick to insect pollinators enabling more pollen to become attached to the insect.Pollen grains are very resistant to chemical and biological degradation such that they can be identified in geological deposits over 100 million years old. Pollen analysis of geological samples reveals the type of vegetation and likely climate prevailing at the time the deposit was laid down. Companies involved in oil exploration employ Palynologists to study pollen and other microfossils in the continuing search for new oilfields.