182 Operation of the Earths in the Process of Vegetation. 



lime, there exists a force which must tend to combine these 

 substances ; the sihca and alumina are electro-negative bodies 

 in respect to the lime, and in their presence the lime must ac- 

 quire the opposite electrical condition. Thus, according as ex- 

 terior movements, which are foreign causes, place the molecules 

 at a greater or less distance, and group them in different man- 

 ners, electrical piles are established, the degrees of tension vvill 

 vary, discharges wiU take place, and the soil will be as it were 

 animated. The electric fluid which pervades it will excite the 

 radicular stomata, and the absorption of the fluids proper to the 

 nourishment of the vegetable will take place ; and the radicular 

 fibres impregnated by humidity will become charged conductors 

 for transmitting electricity to the plant, an electricity which is 

 certainly as necessary to life as light and heat. 



M. Pelletier afterwards considers certain practical operations 

 in agriculture for improving soils, such as the mixture of beds 

 of earth of different kinds, the use of marl, the exposure of 

 marls to the air, tillage, and the use of lime ; and he endeavours 

 to deduce from his theory an exjilanation of the useful effects 

 produced by these operations. He then examines why, at great 

 depths, where he thinks that the oxygen of the air and the car- 

 bonic acid cannot penetrate, the radicles of the old trees can 

 find carbonic acid, which, when absorbed, furnishes the carbon 

 necessary for the nourishment of the vegetable. He admits, 

 seeing the tendency that silica and alumina have for combining 

 with lime, that there is a reaction of these two earths on the cal- 

 careous carbonate, a combination, a formation of a silicate, and 

 a disengagement of carbonic acid. Thus, then, according to 

 M. Pelletier, at certain depths, and under influences hitherto 

 but little known, the silica would decompose the carbonate of 

 lime, while at the surface of the earth, and under the influence 

 of external agents, the silicates would be decomposed by car- 

 bonic acid. 



2. On tlie AlgcE lohich communicate a red cotour to tJi£ waters of 

 some salt marshes, by M. F. Dunal. 



We often perceive in the reservoirs of salt-works, termed 

 tables, water of a beautiful rose colour with a violet reflection, 

 or water having a ferruginous orange-red tint, at the edges of 



