62 ORIGIN AND ACTION OF HUMUS. 



are appended to this work, spare me all further 

 remarks upon its efficacy. 



Plants thrive in powdered charcoal, and may be 

 brought to blossom and bear fruit if exposed to 

 the influence of the rain and the atmosphere ; the 

 charcoal may be previously heated to redness. 

 Charcoal is the most " indifferent " and most un- 

 changeable substance known ; it may be kept for 

 centuries without change, and is therefore not sub- 

 ject to decomposition. The only substances which 

 it can yield to plants are some salts, which it con- 

 tains, amongst which is silicate of potash. It is 

 known, however, to possess the power of condensing 

 gases within its pores, and particularly carbonic acid. 

 And it is by virtue of this power that the roots of 

 plants are supplied in charcoal exactly as in humus, 

 with an atmosphere of carbonic acid and air, which 

 is renewed as quickly as it is abstracted. 



In charcoal powder, which had been used for 

 this purpose by Lukas for several years, Buchner 

 found a brown substance soluble in alkalies. This 

 substance was evidently due to the secretions from 

 the roots of the plants which grew in it. 



A plant placed in a closed vessel in which the 

 air, and therefore the carbonic acid, cannot be 

 renewed, dies exactly as it would do in the vacuum 

 of an air-pump, or in an atmosphere of nitrogen or 

 carbonic acid, even though its roots be fixed in the 

 richest mould. 



