LEAF MOULD. 



295 



LEAF MOULD. 



looking mass remains, consisting of bodies 

 of the humic acid series. When reduced to 

 this state, they are, to all physical appear- 

 ance, like dark -brown soil, or earth ; and 

 it is to their presence that garden soils owe 

 their peculiar colour. On ultimate analysis, 

 these brownish bodies are found to consi-st 

 of hurntCy ttlmic, and geic acids, neither of 

 them soluble in water, but all soluble in 

 alkalies', with which they have a strong 

 affinity. Hence their tendency to unite in 

 the ammonia, and their value as manures 

 in connection with alkali. 



" Not only do they absorb such of this 

 alkali as they come in contact with," says 

 Dr. Scoffern, " but it is suspected that they 

 actually, like many other porous bodies, 

 promote the combination of oxygen and 

 hydrogen, and form ammonia by catalytic 

 agency a term used by Berzelius to express 

 the result of the contact of a third body 

 upon two others, without being itself 

 changed in its character a beautiful pro- 

 vision of Nature, by which the products of 

 natural decomposition are endowed with 

 the properties necessary to render them fit 

 for assimilation as food for vegetables." 

 From this it is clear how important it is 

 that not a leaf should be suffered to run to 

 waste, but should be swept up as they fall, 

 and conveyed to a heap, taking care to 

 keep them by themselves, and apart from 

 other manures, until they are in a state fit 

 for mixing into composts. 



The manner in which these influences 

 operate is an interesting subject to the 

 gardener. The fertilising properties of 

 manure are in proportion to the nitrogen 

 contained in it, this gas being absorbed by 

 plants in combination with hydrogen in the 

 form of ammonia, which is composed of 

 fourteen parts of nitrogen and three parts 

 of hydrogen by weight. When this is borne 

 in mind, and the fact that the atmosphere 

 is another source from which plants derive 

 this substance, the great utility of trenching 



becomes evident, especially to those plants 

 which easily give off their nitrogen to mix 

 in the atmosphere rather than in the soil. 

 Leguminous plants arc valuable in this 

 respect, for it enables the cultivator to 

 enrich the ground which has been ex- 

 hausted by excessive cropping. That the 

 atmosphere holds ammonia sufficient for 

 the development of plants is due to the 

 decomposition of organised bodies, which 

 all contain a greater or less quantity of 

 nitrogen; but it is particularly in the bodies 

 of animals that this agent exists. It enters 

 into the composition of all their organs, 

 and when, after death, animals are left to 

 the chemical action of nature, all the 

 elements of which they were constituted 

 are separated, and immediately form new, 

 and for the greater part, gaseous com- 

 pounds, and amongst them ammonia, 

 which is dissolved in the atmosphere by 

 the water with which the air is always 

 charged. 



Another source of this agent has been 

 traced to the electric discharges in a 

 thunderstorm. Carbonate of ammonia, 

 according to Boussingault and Liebig, pre- 

 exists in ail organised beings. " The 

 phenomenon of the constancy of thunder- 

 storms," M. Boussingault says, "would 

 seem to justify this opinion. It is said, 

 indeed, that every time a series of electric 

 flashes pass in the humid atmosphere, 

 there is a production and combination of 

 nitric acid and ammonia ; the nitrate of 

 ammonia, besides, always accompanies the 

 rain which falls in a thunderstorm ; but 

 this acid being fixed in its nature, cannot 

 be maintained in a state of vapour. When 

 we consider the reaction which takes place 

 between the different compounds in ques- 

 tion, it may easily be conceived that the 

 nitrate of ammonia, which is drawn to the 

 earth by the rain, and which comes in con- 

 tact with the rocks or calcareous soil, is 

 afterwards volatilised to the state of car- 



