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A cow stays close to its calf to make sure it will get everything
it needs to grow. In the grass around their hooves, the fungus Pilobolus
does exactly the opposite. To help its spores, Pilobolus uses a "shotgun"
to blast them as far away as possible.
Pilobolus lives
in cow dung. This life habit may seem terrible to us, but fungi like Pilobolus
are very important in nature. These fungi, called "decomposers"
break down non-living organic matter by feeding on it. Some bacteria and
animals are also decomposers. Without them, we would be surrounded
everywhere by piles of dead plants, animals and dung.
To live in
cow dung, the Pilobolus fungus must first get into the cow's dung.
The cow has to eat the spores of Pilobolus
while grazing. Spores are very tough. The cow cannot digest them. They
pass through the animal's digestive system and are excreted in the dung,
where they will grow.
Pilobolus has evolved a way to
shoot its spores on to the grass. Its "shotgun" is a stalk
swollen with cell sap, bearing a black mass of spores on the top. Below
the swollen tip is a light-sensitive area. The light sensing region
affects the growth of Pilobolus by causing it to face toward the
sun. As the fungus matures, water pressure builds in the stalk until the
tip explodes, shooting the spores into the daylight.
The spores
fly away at 35 feet per second (10.8 m per second), at a height of six
feet (2 m), and land as far away as 8 feet (2.5 m). Pilobolus,
without knowing it, can shoot over a cow.
Shooting the spores
into the daylight gives them a better chance of landing in a sunny place
where grass or other plants are growing. The cows that made the dung for
the previous batch of Pilobolus will probably eat these spore
covered plants and start the process all over again.
GLOSSARY
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Last
update: 5 Sep 96. © 1996, Robert Fogel, Ivins, UT 84738. Edited by Patricia Rogers. Photograph courtesy of M.J. Wynne