264 ACTION OF PLANTS ON THE SOIL. 



sulfureus and various other fungi, the red-rot, &c., all depend on similar disruptions 

 of the organic compounds in dead plants, and result in the ultimate dispersal of 

 these in the air in the form of carbon-dioxide, ammonia, nitric acid, and water. 



Thus, ultimately, the exercise of this destructive activity only effects a return of 

 the compounds just enumerated — the most important to plant-life — to the regions 

 whence they had previously been withdrawn by the plants when living. Carbon 

 and nitrogen, in particular, are set free from their bonds and given back to the 

 atmosphere in the form and combination in which they are capable of being 

 appropriated anew by living plants as food-materiaL 



Considered from this point of view the phenomena of putrefaction and rotting 

 appear as important and even necessary incidents in the history of the substances 

 which are of the greatest importance to plants. Abhorrence of putrefaction is 

 innate in us all, and everything connected with it — in particular, the entire race of 

 bacteria — is looked upon with aversion. To estimate these processes according to 

 their deserts requires a sort of self-abnegation. But when we overcome our 

 repugnance and weigh the whole subject impartially, we come to the conclusion that 

 the continued existence of vegetable life and of life in general depends upon the 

 occurrence of putrefaction. If the untold numbers of plants which die in the course 

 of a year did not rot sooner or later, but remained unchanged as lifeless forms, a 

 certain quantity of carbon and nitrogen would be idle, being withdrawn from the 

 sphere of activity and locked up, so to speak. Now, assuming this to be repeated 

 year by year, a time must come when all the carbon and nitrogen would be 

 imprisoned in dead plants. Thereupon, all life would cease, and the whole earth 

 would be one great bed of corpses. 



Not only putrefaction, but also the minute organisms which excite putrefaction 

 appear in a more favourable light when viewed from this standpoint. Let such 

 bacteria as act in the capacity of foes to the human race, ravaging town and 

 village in the form of infectious diseases, be exterminated if possible; but annihila- 

 tion of putrefactive bacteria would mean a disastrous interference with the cycle of 

 life upon the earth. These latter are not to be reckoned as enemies but friends to 

 human beings. The effect of their invasion of dead plants and animals is certainly 

 first made manifest, not in the most agreeable manner, for some of the substances 

 mentioned as being evolved in the early stages of the onslaught, viz.: various 

 ammoniacal compounds, sulphuretted hydrogen, and the volatile fatty acids, are 

 disgusting to us; but as decomposition advances these phenomena, which are so 

 unpleasant to our senses, abate, and the action of putrefactive bacteria becomes 

 ultimately a beneficent process of purification of the last remnants of dead 

 organisms. The final result of the decomposition of organic bodies by bacteria has 

 been termed mineralization. It is a fact that nothing is ultimately left behind, in 

 the ground or water, of bodies decomposed by the indefatigable exertions of bacteria 

 excepting some nitric acid and the small quantity of mineral food-salts which has 

 been taken up by the living organism in its time and are now in the form of dust 

 and ash. 



