Page:The aquarium - an unveiling of the wonders of the deep sea.djvu/30

Rh so novel as I had at first supposed. Priestley first advanced the opinion that plants in certain circumstances emitted oxygen gas; and Ingenhousz soon after discovered that the leaves of plants, when immersed in water, and exposed to the light of day, produced an air, which he announced as oxygen gas. This result, however, was doubted by Ellis, in his elaborate treatise on Atmospheric Air, and, as he considered, disproved. The consumption of oxygen by animals in respiration, and the emission of carbonic acid from the lungs and skin, were well shown by this writer, who maintained, however, that this latter gas was also emitted by the leaves of plants.

At the third Meeting of the British Association, held at Cambridge in 1833, Professor Daubeny communicated a notice of certain researches which he was then pursuing, concerning the action of light upon plants, and that of plants upon the atmosphere. "He considered that he had established, by experiments on plants immersed, sometimes in water impregnated with carbonic acid gas, and at others in atmospheric air containing a notable proportion of the same, that the action of light in promoting the discharge of certain of their functions, and especially that of the decomposition of carbonic acid, is dependent neither upon the heating, nor yet upon the chemical energy of the several rays, but upon their illuminating power.

"He regarded light as operating upon the green parts of plants as a specific stimulus, calling into action, and keeping alive those functions, from which