It is likewise found that the _perspiration_ of vegetables is increased or diminished, in a certain measure by the degree of _light_ which falls upon them. The experiments of Mr. P. Miller and others, prove that plants uniformly perspire most in the forenoon, though the temperature of the air in which they are placed should be unvaried. M. Guettard likewise informs us that a plant exposed to the rays of the sun, has its perspiration increased to a much greater degree than if it had been exposed to the same heat under the shade. Vegetables are likewise found to be indebted to light for their smell, taste, combustibility, maturity, and the resinous principle, which equally depend upon this fluid. The aromatic substances, resins, and volatile oil are the productions of southern climates, where the light is more pure, constant, and intense. In fine, another remarkable property of light on the vegetable kingdom is that, when vegetables are exposed to open day-light, or to the sun’s rays, they emit oxygen gas or vital air. It has been proved that, in the production of this effect, the sun does not act as a body that heats. The emission of the gas is determined by the light: pure air is therefore separated by the action of light, and the operation is stronger as the light is more vivid. By this continual emission of vital air, the Almighty incessantly purifies the atmosphere, and repairs the loss of pure air occasioned by respiration, combustion, fermentation, putrefaction, and numerous other processes which have a tendency to contaminate this fluid so essential to the vigor and comfort of animal life; so that, in this way, by the agency of light, a due equilibrium is always maintained between the constituent parts of the atmosphere.