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Geranium
The size of the grains is measured in millionths of a meter, but the romantic journeys of pollen are epic. The dozens of golden grains that have successfully reached a Geranium phaeum flower's stigma must compete to be among the few that achieve fertilization.
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Snowball blossom
Lodged in the rumpled tissue of a Viburnum tinus stigma, pollen grains from other snowball blossoms (gray) swell with moisture. One (at center) is already growing the tube that delivers sperm to the ovule. Other species' pollen (yellow and green) has landed amiss; genetic defenses exclude them from the fertilization race.
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Willow
A grain of Salix caprea pollen has missed its mark. Wedged between flower petals, it will die. While some grains will be flung into the air as springtime breezes swirl the willow leaves, others will stick to the backs of bees and find their way.
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Composite image by Martin Oeggerli; 14 SEM scans by Ralf Buchner and Heidemarie Halbritter, University of Vienna
Pollen comes in many forms and sizes. The diameter of a pumpkin pollen grain (at center) is as thick as a dollar bill. The tiny speck at its lower right is a grain of forget-me-not pollen.
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Flowering quince
The convoluted surface of Chaenomeles sp. pollen may speed up moisture absorption when the grain lands on a target bloom. "Quick hydration means faster formation of the pollen tube," says Swiss photographer Martin Oeggerli, a postdoctoral fellow at University Hospital Basel. "That's important for fertilization."
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White clover
Trifolium repens
White clover's protein-rich pollen is an important food for bees, as is its nectar.
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Indian mallow
Abutilon pictum
Spines on Indian mallow pollen help it cling to bird feathers.
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Bromeliad
Tillandsia maxima
The fold in a bromeliad grain allows it to shrink as it dries, or swell with moisture, without breaking.
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Water cabbage
Pistia stratiotes
The ridges on water cabbage grains are an unusual pollen surface feature, though the plant is common from Egypt to Argentina.
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Forget-me-not
Myosotis sylvatica
Forget-me-not grains are among the tiniest known, each just five one-thousandths of a millimeter across.
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Venus flytrap
Dionaea muscipula
Venus flytrap grains are more than 15 times bigger than forget-me-not ones: There's no consistent correlation between plant and pollen size.
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Persian silk tree
Albizia julibrissin
Persian silk tree grains are also more than 15 times bigger than forget-me-not ones.
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Silver leaf tree
Proteaceae
Silver leaf tree grains have a sticky coating that bonds them to animal carriers.
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Poison bulb
Crinum japonicum
Poison-bulb pollen is surrounded by long, showy petals that attract insect porters. Some variations seem easy to explain. Others remain puzzling, or have yet to be investigated at all.
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Pine
The pollen of this family coats cars with yellow-green dust—though this particular grain landed on an unhatched insect egg. It floats through the air, sperm carried by two pale "balloons." Such wind-borne pollen causes misery for allergy sufferers in much of the world, where it falls heavily, as it has for millions of years.
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