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Surprises in the Pasture

Surprises in the Pasture


Have you walked in a pasture lately, closely examining some fresh cow dung? A delightful little fungus grows there. It is so interesting you will wish to give it more than a fleeting glance.

It seems a pity that such an interesting fungus as Pilobolus should grow in such an unsavoury location. In actual fact however, the beauty of Pilobolus is that it is so well designed for this habitat. Thin white threads of mold run over and into the surface of fresh horse and cow droppings.

Standing erect from the growing surface are other threads more than 1 cm tall. These erect threads consist of a bulgy section at the bottom and another at the top of the thread. Sitting on top of the uppermost bulge is a heavy black cap.

The whole purpose of the upright portion of the fungus is to make sure that a cow or horse eats the spores. The difficulty from the fungus’ point of view is to get from the dung, where it grows but which the animals will not eat, onto the grass which the animals do eat. Once on the grass, the spores are duly consumed and they then pass through the unsuspecting animal. Thus the spores are ideally situated to develop on the freshly deposited manure.

As far as the upright fungus thread is concerned, the lowermost bulb is sensitive to light. This bulge seems to act as a lens, focusing the light on some kind of pigment. In response, the thread bends towards the light. This ensures that the threads are pointing towards grass and away from more manure.

The bulb at the upper end has quite a different function. It sits immediately below the spore containing body. These spores are protected by a heavy black cap. Eventually a cell layer dissolves between the upper bulb and the spore containing structure above. Immediately the bulb contracts, squirting a jet of cell sap together with the dark spore cap. These latter sail into the air at an average initial speed of 10.8 m/sec (35 feet/second), flying to a distance of up to 200 cm (6.5 ft) from the manure.

It is truly amazing that so tiny a structure can achieve such force! The spores inside the cap generally end their journey by landing and sticking to a blade of grass. It seems obvious that Pilobolus is carefully designed to suit this habitat. Without the elegant ejecting mechanism, few if any spores would reach the fresh dung. It seems hard to imagine how such a system could have developed gradually through selection from chance variation. Is it not interesting how nature testifies to the Creator?

Margaret Helder
December 2004

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