DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY DENNIS KUNKEL MICROSCOPY / SCIENCE PHOTO LIBRARY
Sunflower petal with two pollen grains (Helianthus sp.), coloured environmental scanning electron micrograph (ESEM). The outer wall (exine) has many small spiky projections. The pollen gets caught in the body hairs of insects visiting the flower. Cross pollination occurs when insects fly to another similar flower and pollen is left behind. Pollen contains the male reproductive cells of a plant. When the pollen grain, containing the male gametes, lands on the stigma of a flower, it germinates. A pollen tube grows out from the germinal pore, down through the stigma, to the ovary. The male nuclei pass down the tube, fertilize the ovules and seed is formed. Humans can also be allergic to daisy pollen. Magnification: x365 when shortest axis printed at 25 millimetres.
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