150 THE ART OF CULTURE. 



kinds of plants grow with the greatest luxuriance. 

 This fertility is owing to the alkalies which are con- 

 tained in the lava, and which by exposure to the 

 weather are rendered capable of being absorbed by 

 plants. Thousands of years have been necessary to 

 convert stones and rocks into the soil of arable land, 

 and thousands of years more will be requisite for 

 their perfect reduction, that is, for the complete ex- 

 haustion of their alkalies. 



We see from the composition of the water in riv- 

 ers, streamlets, and springs, how little rain-water is 

 able to extract alkali from a soil, even after a term 

 of years ; this water is generally soft, and the com- 

 mon salt, w^hich even the softest invariably contains, 

 proves, that those alkaline salts, which are carried 

 to the sea by rivers and streams, are returned again 

 to the land by wind and rain. 



Nature itself shows us what plants require at the 

 commencement of the development of their germs 

 and first radicle fibres. Becquerel has shown, that 

 the graminecB) leguminoscB, cruciferce, cichoracece, urn- 

 bellifercBj coniferce, and cucurbitacece emit acetic acid 

 during germination. A plant which has just broken 

 through the soil, and a leaf just burst open from the 

 bud, furnish ashes by incineration, which contain as 

 much, and generally more, of alkaline salts than at 

 any period of their life. (De Saussure.) Now we 

 know also, from the experiments of Becquerel, in what 

 manner these alkaline salts enter young plants ; the 

 acetic acid formed during germination is diffused 

 through the wet or moist soil, becomes saturated 

 with lime, magnesia, and alkalies, and is again ab- 

 sorbed by the radicle fibres in the form of neutral 

 salts. After the cessation of life, when plants are 

 subjected to decomposition by means of decay and 

 putrefaction, the soil receives again that which had 

 been extracted from it. 



Let us suppose, that a soil has been formed by the 

 action of the weather on the component parts of 

 granite, grauwacke, mountain limestone, or porphy- 



