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 214 to be excessively luxuriant in vegetation. Plants also give out azotic gas: but M. de Saussure is of opinion that this proceeds from their internal substance; and it appears by his experiments to be rather a sign of disease or approaching decay, than a regular chemical production of their constitution when in health; for Sennebier found the quantity of oxygen emitted was in proportion to the thickness of the leaf, or quantity of parenchyma. Yet the parenchyma must be in its original organized state, for when bruised its functions are destroyed.

Possibly such an alternation in the functions of vegetables between day and night may afford a necessary repose to their vital principle, whose share in them we know to be of primary importance. Whatever may happen to plants in the dark, there can be no doubt of their principal business in the œconomy of nature being what we have described. The most luminous and compendious view of the whole subject is given by Dr. Thomson of Edinburgh in the fourth vol. of his Chemistry, which is well worth the attention of those who wish to enter more