146 THE ART OF CULTURE. 



yet it is well known, that when the volcanic ashes 

 have been exposed for some time to the influence 

 of air and moisture, a soil is gradually formed in 

 which all kinds of plants grow with the greatest 

 luxuriance. This fertility is owing to the alkalies 

 which are contained 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 exhaustion of 

 their alkalies. 



We see from the composition of the water in 

 rivers, 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 

 common salt, which 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. Bequerel has shown that 

 the graminece, leguminostz, crucifertz, cichoracece, 

 unibellifercz, coniferce, and cmurbitacece 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 



