Did You Know?

In hydrotropism, a plant's roots grow in the direction of increasing moisture, hoping to obtain water. In phototropism, a plant (or fungus) moves toward light, usually the sun—perhaps because, in the colder climates where such plants are usually found, concentrating the sun's warmth within the sun-seeking flower can create a warm and inviting environment for the insects that fertilize it. In thigmotropism, the organism moves in response to being touched; most climbing plants, for example, put out tiny tendrils that feel around for something solid and then attach themselves or curl around it. When microbiologists talk about tropism, however, they're often referring instead to the way a virus will seek out a particular type of cell to infect. And when intellectuals use the word, they usually mean a tendency shown by a person or group which they themselves might not even be aware of.