Massee : TJic Action of Bacteria on Higher Plants. 69 



The complete transformation is carried out in three stages : — 



(1) The organic matter — manure — is broken up, and, 

 among- other substances, nitrogen and ammonia are 

 liberated. The nitrogen escapes into the air, when 

 a portion of it can be directly utilised by certain Bacteria, 

 in a manner to be dealt with later. One of the most 

 active of Bacteria engaged in this work is Bacterium 

 mycoides. 



(2) Next, a group of active workers known as Nitrite- 

 Bacteria make it their business to convert the ammonia 

 liberated by the work of the first group into nitrous acid. 



(3) A third group of Bacteria convert the nitrous acid 

 into nitric acid. Now this free nitric acid displaces other 

 acids from their combination with either sodium or 

 potassium, and takes their place, forming either nitrate 

 of potash or nitrate of soda. Both these last-named 

 substances dissolve in water, and are taken up by the 

 roots of plants, and, broadly speaking, may be said to 

 be the only two substances which directly furnish all 

 flowering plants (except the pea tribe and a few others 

 having tubercles on the roots) with the nitrogen they require. 



The groups of Bacteria engaged in the formation of nitrate 

 of potash and nitrate of soda, as described above, are collectively 

 spoken of as nitrifying Bacteria ; and when we take into con- 

 sideration the absolute necessity of nitrogen in some available 

 form for the support and continuance of plant life on the globe, 

 and, furthermore, the great cost of nitrogenous fertilisers, it 

 will be seen how important it is to afford every opportunity 

 of enabling those minute organisms to carry on their work, as 

 on its continuance depends the very existence of all the higher 

 forms of life on the earth. 



All the nitrifying Bacteria are aerobic, or, in other words, 

 require to be in contact with free oxygen. They are also very 

 susceptible to water — a certain amount is necessary for their 

 well-being, too much is prejudicial. An excess of free acid in 

 the soil is also very injurious. 



A fertile soil means the presence of nitrifying Bacteria living 

 under those conditions which enable them to do the maximum 

 of work. These conditions can be secured by good tillage, 

 which secures the free access of oxygen to the soil ; good 

 drainage, without which the soil cannot possibly be aerated ; 

 and the neutralisation of all tendency to acidity or sourness by 

 the free use of lime. 



1904 March i. 



