1108. Light is a body which has very considerable influence on the structure of vegetables, and some also on their habitation. The Fungi do not require the usual interludes of day, in order to decompose carbonic acid gas, and can live and thrive with little or no light. In green plants, which require the action of light, the intensity required is very different in different species : some require shady places, and hence the vegetable inhabitants of caves, and the plants which grow in the shade of forests ; others, and the greater number, require the direct action of the sun, and grow in exposed elevated sites. De Candolle considers that the great difficulty of cultivating Alpine plants in the gardens of plains, arises from the impossibility of giving them at once the fresh temperature and intense light which they find on high mountains.
