The diffusion of _electrical_ matter, found in the air and in all other substances, furnishes a presumption, that it is an efficient agent in vegetation. Nollet and others have thought that, artificially employed, it favoured the germination of seeds and the growth of plants; and Mr. Davy "found, that corn sprouted more rapidly in water, _positively_ electrified by the voltaic battery, than in water _negatively_ electrified."[8] These opinions have not escaped contradiction, and _we_ do not profess to decide where doctors disagree. [8] Davy's Elements. 5th. Of _stable yard manures_, _lime_, _marl_, and _gypsum_, and their agency in vegetation: We have already said, that vegetables in the last stage of decomposition, yield a black or brown powder, which Mr. Davy calls "_a peculiar extractive matter, of fertilizing quality_," and which the chymists of France have denominated _terreau_. This vegetable residuum is the simple mean employed by nature to re-establish that principle of fertility in the soil, which the wants of man and other animals are constantly drawing from it. It was first analyzed by Hassenfratz, who found it to contain an oily, extractive and carbonaceous matter, charged with hydrogen; the acetates and benzoates of potash, lime and ammoniac; the sulphates and muriates of potash, and a soupy substance, previously noticed by Bergman.--Among other properties (and which shows its combustible character) is that of absorbing, from atmospheric air, its oxygen, and leaving it only azote. This was discovered by Ingenhouse, who, with De Sausure and Bracconnet, pursued the subject by many new and interesting experiments, the result of which is-- 1. That the oxygen thus absorbed, deprives the terreau of part of its carbon, which it renders soluble and converts into mucilage; and 2. That the carbonic acid, formed in the process, combines with the mucilage, and with it is absorbed by the roots of plants. If we put a plant and a quantity of slacked lime under the same receiver, the plant will perish; because the lime will take from the atmospheric air all the carbonic acid it contains, and thus _starve_ the plant. Vegetables, placed near heaps of lime in the open air, suffer from the same cause and in the same way; but though lime, in _large_ quantities, destroys vegetation, in _small_ quantities it renders vegetation more vigorous. Its action is of two kinds--mechanical and chymical; the first is a mere division of the soil by an interposition between its parts; the second, the faculty of rendering soluble vegetable matter, and reducing it to the condition of terreau. The _mechanical_ agency ascribed to lime, belongs also to _marle_ and to _ashes_, and in an equal degree--but their _chymical_ operation, though similar, is less.[9] [9] Vegetable ashes are _lime_, combined with an earthy saline matter.