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How a Hairy-cap Avoids Too Strong Light

The devices for avoiding the extreme heat of the sun are perhaps still more wonderful than those for obtaining a sufficient amount. It is a fact that in the leaves of the Hairy-caps only the upper surface of the leaves is so constructed as to be injured by too dry heat. The cell walls of the lower surfaces are on the contrary thick and impervious to water, so that they cannot give up moisture to the air when it is dry, a character which insures against loss by evaporation, for when the air is dry the mosses simply turn the awn-pointed leaves upwards with the points and the impervious under-surfaces to the sun and the delicate cells toward the stem.