348 On Paring and Burninf/. 



brought into contact with atmospheric air, the oxygen of which 

 changes them by degrees into brown and black humus, both of 

 which include various organic combinations, characterised by- 

 great avidity for absorbing oxygen from the atmosphere, hy which 

 they are finally resolved into carbonic acid. Organic matters 

 tlius furnish a continual source of carbonic acid in the soil, and 

 afford thereby organic food to the plant, which food appears to 

 be highly beneficial in the earliest stages of vegetable life, 

 before the green leaf is fully formed, and the more mature plant 

 can avail itself of the rarbt)nic acid of the atmosphere. 



5. This process of slow oxidation, or eremacausis, to which 

 all organic matters are subject in contact with the air, is at- 

 tended with evolution of heat, which heat, of course, is bene- 

 ficial to the growth of plants. 



6. In virtue of the dark colour of humus, soils containing 

 organic matters absorb more readily heat from the sun than 

 others deficient in humus ; and for this reason also organic 

 matters appear to favour vegetable growth. 



7. The vegetable remains of former crops, besides combustible 

 elements, contain mineral matters : the latter, however, are so 

 firmly united with the organic portion that they cannot be dis- 

 solved by water from the fresh organic matters. But in the 

 measure in which the decomposition of the organic matter pro- 

 ceeds, the mineral matters are rendered soluble, and thus humus 

 furnishes also mineral food to the growing plant. 



For more than one reason, therefore, organic matters in the soil 

 are capable of exercising a beneficial influence on plants. It 

 may appear therefore highly desirable to preserve them by all 

 means ; and their destruction by fiie would seem to be opposed 

 to t!ie first principles of good farming. There can be no doubt 

 that, in many instances, paring and burning is inapplicable ; but 

 at the same time experience has shown that in other instances 

 the destruction of the organic matter in soils is not attended with 

 any evil consequences. There must exist therefore some cause 

 or causes which afford an explanation of the benefits of a practice 

 which appears contrary to what has been stated in regard to the 

 functions of humus. Now it is quite true that humus absorbs 

 moisture and ammonia from the atmosphere, but is it equally 

 true that all soils stand in need of a good absorber of moisture 

 and ammonia? Are there not some which seldom get ev-en suffi- 

 ciently dry, and for this reason are considered wet and cold soils? 

 Are there not soils which contain constituents capable, like organic 

 matter, of absorbing moisture and ammonia from the atmosphere 

 and of retaining it? Again, are there not plants whicli find 

 abundance of organic food in the atmosphere, and for this reason 

 are not dependent for food on the organic matter in the soil? It is 



