Mr. Humboldt diſcovered, in 1793, that ſimple metallic ſubſtances are unfavourable to the germination of plants,and that metallic oxydes favour it in proportion to their degrees of oxydation. This diſcovery induced him to ſearch for a ſub- ſtance with which oxygen might be ſo weakly combined as to be eaſily ſeparated, and he made choice of oxygenated muriatic acidgas mixed with water. Creſſes (lepidium ſativum) in the oxygen-ated muriatic acid ſhewed germs at the end of ſix hours, and in common water at the end of 32 hours. The action of the firſt fluid on the vegetable fibres is announced by an enormous quanti-ty of air bubbles which cover the ſeeds, a phenomenon not exhib-ited by water till at the end of from 30 to 45 minutes. Theſeexperiments announced in Humboldt’s Flora Subterranea Friberg-enſis, and in his Aphoriſms on the chemical phyſiology of Plants, have been repeated by others.See Uſlar’s Fragments of Phythology, Plenck’s Phyſiology, Villdenow’s Dendrology, and Dictionnaire de Phyſique par Gehler. They were made at a tempera-ture of from 12 to 15 Reaumur. In the ſummer of 1796, Hum-boldt began a new ſeries of experiments, and found that by join-ing the ſtimulus of caloric to that of oxygen he was enabled ſtill more to accelerate the progreſs of vegetation. He took the ſeeds of garden creſſes (lepidium ſativium,) peas (piſum ſativum,) French beans (phaſeolus vulgaris,) garden lettuce (lactuca ſativa,) mignon-ette (reſeda odorata;) equal quantities of which were thrown in-to pure water and the oxygenated muriatic acid at a tempera-ture of 88° F. Creſſes exhibited germs in three hours in the oxy-genated muriatic acid, while none were ſeen in water till the end of 26 hours. In the muriatic nitric The nitric acid, however, diluted with a great deal of water, accelerates germination alſo, according to the experiments of Can-dolle, a young naturaliſt, who has applied with great ſucceß to vegetable phyſiology. This phenomenon is the more intereſting, as chemiſtry affords other analogies of the oxygenated muriatic acid and the nitric acid. Profeſſor Pfaß Pfaff , at Kiel, by purſuing Humboldt’s experiments, has found that frogs ſuffocated in oxy-genated muriatic acid gas increaſe in irritability, while thoſe which periſh in carbonic acid gas are leß ſenſible of Galvaniſm. or ſulphuric acid, pure or mixed with water, there was no germ at all: the oxygen ſeemed there to be intimately united with baſes of azot or ſulphur, to be diſengaged by the affinities preſented by the fibres of the vege-table. The author announces that his diſcoveries may one day be of great benefit in the cultivation of plants. His experiments have been repeated with great induſtry and zeal by ſeveral diſ-tinguiſhed philoſophers. Profeſſor Pohl at Dreſden cauſed to germinate in oxygenated muriatic acid the ſeed of a new kind of euphorbia taken from Bocconi’s collection of dried plants, 110 or 120 years old. Jacquin and Vander Van der Schott at Vienna threw into oxygenated muriatic acid all the old ſeeds which had been kept 20 or 30 years at the botanical garden, every attempt to produce vegetation in which had been fruitleß, and the greater part of them were ſtimulated with ſucceſs. Even the hardeſt ſeeds yield-ed to this agent. Among thoſe which germinated were the yel-low bonduc or nickar tree (guilandina bonduc,) the pigeon cytiſus or pigeon pea (cytiſus cajan,) the dodonea anguſtifolia, the climbingmimoſa (mimoſa ſcandens,) and new kinds of the homea.—There are now ſhewn at Vienna very valuable plants which are entirely owing to the oxygenated muriatic acid, and which are at preſent from five to eight inches in height. Humboldt cauſed to germi-nate the cluſia roſea, the ſeeds of which had been brought from the Bahama iſlands by Booſe, and which before had reſiſted every effort to make them vegetate. For this purpoſe he employed a new proceß, which ſeems likely to be much eaſier for gardeners who have not an opportunity of procuring the oxygenated mu-riatic acid: He formed a paſte by mixing the ſeeds with the black oxyde of manganeſe, , and then poured over it the muriatic acid diluted with water. Three cubic inches of water were mixed with half a cubic inch of the muriatic acid. The veſſel which contains this mixture muſt be covered, but not cloſely ſhut: elſe it might readily burſt. At the temperature of 95° the muriatic acid be-comes ſtrongly oxydated; the oxygenated muriatic gas which is diſengaged paſſes through the ſeeds; and it is during this paſſage that irritation of the vegetable fibres takes place.