9. _Light is found to produce a remarkable effect on Plants and Flowers, and other vegetable productions._ Of all the phenomena which living vegetables exhibit there are few that appear more extraordinary than the energy and constancy with which their stems incline toward the light. Most of the discous flowers follow the sun in his course. They attend him to his evening retreat, and meet his rising lustre in the morning with the same unerring law. They unfold their flowers on the approach of this luminary; they follow his course by turning on their stems, and close them as soon as he disappears. If a plant, also, is shut up in a dark room, and a small hole afterwards opened by which the light of the sun may enter, the plant will turn towards that hole, and even alter its own shape in order to get near it; so that though it was straight before, it will in time become crooked, that it may get near the light. Vegetables placed in rooms where they receive light only in one direction, always extend themselves in that direction. If they receive light in two directions, they direct their course towards that which is strongest. It is not the _heat_ but the _light_ of the sun which the plant thus covets; for, though a fire be kept in the room, capable of giving a much stronger heat than the sun, the plant will turn away from the fire in order to enjoy the solar light. Trees growing in thick forests, where they only receive light from above, direct their shoots almost invariably upwards, and therefore become much taller and less spreading than such as stand single.