A matter of give and take

Most flowering plants produce seeds that have a built-in food supply to help the young seedling in the early stages of its life. But the orchid Dactylorchis purpurella is an exception. Its seeds are so tiny that there is no room for a food store. The seed of this flower survives only because of its relationship with a particular kind of fungus, which feeds it and helps it to germinate.

The fungus, a species of the Rhizoctonia family, penetrates the seed and provides it with nutrients from the soil until it has grown leaves that can produce their own food through photosynthesis. As the orchid develops, the fungus takes nourishment from the orchid's roots. The two plants live side by side, in what at first appears to be a mutually beneficial relationship.

But as the orchid takes the nutrients it needs, it actually eats away at the fungus. Eventually, when the orchid can depend on its leaves to provide enough food, it devours its life-giving partner completely.