ON H.vrvVESTING SOILS AND COMPOSTS. 525 



cnaracter, — a beauti/"ul provision 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."* These remarks will show how im- 

 portant 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. 



1637. The manner in which these influences operate is an interesting subject 

 to the gardener. 



1638. The fertilizing properties of manure being in proportion to the 

 nitrogen or azote contained in it, and this gas being absorbed by plants, in 

 combination with hydrogen in the form orf ammonia, — and the atmosphere, 

 after the sources we have described are exhausted, being another source from 

 which plants derive this substance, the gi-eat utility of trenching becomes 

 evident, especially to those plants which easily give off their azote to mix in 

 the atmosphere rather than in the soil. Leguminous plants are valuable in 

 this respect, for it enables the cultivator to enrich the ground which has been 

 exhausted by excessive cropping. 



1639. '^^^ cause of the atmosphere holding ammonia suflScient for the deve- 

 lopment of plants is the decomposition of organized bodies, which all contain 

 a greater or less quantity of azote ; 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 

 natm-e, all the elements of which they were constituted are separated, and 

 immediately form new, and for the greater part, gaseous compounds, and 

 amongst them ammonia, which is dissolved in the atmosphere by the water 

 with which the air is always charged. 



1640. Another source of this agent, as we leani from a writer in the Revue 

 Horticole, is in the electric discharges in a thunderstorm. Carbonate of 

 ammonia, according to Boussingault and Liebig, pre-exists in all organized' 

 beings. " The phenomenon of the constancy of thunderstorms/' M. Bous- 

 singault 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 dif- 

 ferent compounds in question, 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 volatilized to the state of 

 carbonate at the next drying of the soil. There can be no doubt at the pre- 

 sent day, that the carbonate of ammonia is the most active agent of vege- 

 tation, and without which all the others would be useless ; but this carbonate 



♦ Handy-Book of the Chemistry of Soils. 



