44 AGRICULTURE. 



caped contradiction, and we do not profess to decide 

 where philosophers disagree. 



V. Of stable manures, and of lime, marl, and gyp- 

 sum, and their agency in vegetation. 



We have already said that vegetables in the last 

 stage of decomposition yield a black or brown pow- 

 der, which Davy calls " a peculiar extractive matter 

 of fertilizing quality," and which the chy mists of 

 France have denominated terreau.* This vegetable 

 residuum is the simple mean employed by nature to 

 re-establish thaf principle of fertility in the soil 

 which the wants of man and other animals are con- 

 stantly drawing from it. It was analyzed by Hes- 

 senfratz, who found it to contain an oily, extractive, 

 and carbonaceous matter, charged with hydrogen ; 

 the acetates and benzoates of potash, lime, and am- 

 moniac ; the sulphates and muriates of potash, and 

 a soapy substance, previously noticed by Bergman. 

 Among other properties (and which shows its com- 

 bustible character) is that of absorbing from atmo- 

 spheric air its oxygen, and leaving it only azote. 

 This was discovered by Ingenhouse, who, with De 

 Saussure and Braconnet, pursued the subject by 

 many new and interesting experiments, the result of 

 which is, 



1. That the oxygen thus absorbed deprives the 

 terreau or extractive matter of part of its carbon, 

 which it renders soluble and converts into muci- 

 lage ; and, 



2. That the carbonic acid formed in the process 

 combines with this mucilage, and with it is absorb- 

 ed by the roots of plants. 



If we put a plant and a quantity of slackened 

 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 lirne in the 



* De Candolle and Macaire call it humus, and Dance and 

 others geine. J. B. 



