THE NUTRITION OF THE ROOT 59 



In the use of stable manure, 

 a mixture of animal excrements and litter, our chief object is 

 to use it to its best advantage. This is only possible if we 

 allow the constantly occurring processes of decomposition to 

 run their proper course. This they will do if a sufficient 

 amount of oxygen is present. Then certain processes of oxida- 

 tion are set up, which we term decomposition, or which, in 

 the case of nitrogenous substance, we sometimes describe as 

 decaying. If, however, the supply of oxygen is deficient or 

 ceases entirely, other processes will take place, and the products 

 of these are often injurious to plant life. 



The above processes of decomposition, which take place b}^ 

 the agency of bacteria, break up the organic substances into 

 carbonic acid, water, ammonia, and free nitrogen, which sub- 

 stances are partly given off as gases, leaving the mineral con- 

 stituents in an easily assimilated form. The ammonia is 

 transformed by bacteria into nitric acid ; the formation of 

 carbonic acid takes place even in the absence of oxygen, but 

 is more plentiful up to a certain degree in the presence of 

 oxygen. 



Light and heat are, of course, not without their effect. But 

 while light acts in such a way as to retard the formation of 

 nitric acid, probably because the formative bacteria are averse 

 to light, the increase of temperature up to T^y" C. causes an 

 increased amount of nitrification (formation of nitric acid) to 

 take place. The maximum evolution of carbonic acid takes 

 place about 60° C. 



Moisture also furthers the decomposition of organic snb- 



of manuring by the substances most widely used, and this only in so far as it 

 is of importance in the understanding of the physiological processes of the 

 plant. The same is true of other portions of the subject which belong more 

 especially to the chemistry of agriculture. 



