CARBON. 49 



their growth, will be shown under the head of 

 Humus in Soils. Carbon forms from forty to 

 fifty per cent, by weight of the different 

 cultivated plants, so that in the economy of 

 their growth, it may be considered one of the 

 most important elements of their composition. 

 This is one of the elements the farmer need not 

 trouble himself in applying to his soil as a manure, 

 because the atmosphere furnishes an abundant 

 supply free of cost. The fact of the assimila- 

 tion of carbon by plants from the atmosphere 

 has been placed beyond doubt, by the investiga- 

 tions of eminent scientific men, from the time 

 of Priestley, who made this discovery in 1771, up 

 to the present time. 



The former must not infer from the fact that 

 the atmosphere furnishes to the plant all the 

 carbon which it requires, that the presence of a 

 mould of humus, or partially oxidized organic 

 matter, is not necessary in a soil. Its presence 

 produces beneficial physical effects, that tend 

 directly to their healthy growth. Its capacity 

 for absorbing fertilizing gases and giving them 

 out as they are needed by plants, also its power 

 of attracting heat and retaining moisture, are 

 advantages obtained by the presence of a large 

 amount of mould in the soil, which are not 

 possessed by soils composed simply of sand, no 

 matter how fine the state of division may be, or 



