159 



in the case of nitrosomonas, promoted by the addition of a 

 moderate quantity of sodium bi-carbonate, but is hindered by 

 sodium carbonate. It is also hindered by a large amount of 

 ammonia. Hence, if a large amount of ammonia is present it 

 must first be converted almost entirely into nitrites before nitrates 

 can be formed. 



The importance of these results is obvious. They place at 

 once upon a sound scientific basis the practice of adding manures 

 containing ammonia, nitrites or nitrates, the ultimate product 

 being always nitrates, provided that the conditions necessary for 

 the life of the working organisms are present. But these results 

 also tell us that there may be conditions, such as, for instance, 

 the absence of either or both of the organisms, or the presence 

 of sodium carbonate, which will either entirely stop or, to a great 

 extent, hinder these necessary processes. Under such conditions, 

 plant life will not flourish. 



Recent investigations show, too, that water may play a more 

 important part than has been generally supposed. It is a recog- 

 nised fact that nitrification takes place more readily in light soils 

 than in strong ones, and this is generally attributed to the more 

 easy penetration of air into the former, air being necessary 

 for the life and work of the bacteria. Schloesing, in a paper 

 published in the " Comptes Rendus" (vol. 125), points out that 

 in strong soils, the particles of which are extremely fine, the 

 thickness of the layer of water surrounding each particle is less 

 than the thickness of that surrounding each particle in a light 

 soil (containing the same amount of water), the particles of 

 which are larger, because the total surface in the former case is 

 greater than in the latter. In a series of experiments he showed 

 that by slightly increasing the quantity of water soils in which 

 nitrification took place imperfectly became immensely improved 

 in that respect, nitrification taking place completely. He draws 

 the conclusion that the action of the organism is in some way 

 connected with the thickness of the layer of water surround- 

 ing the particles of the soil, but it is impossible in the small 

 space of an address such as this to explain his reasoning fully. 



Warington, in his researches, found that the bacteria to which 

 reference has been made would not grow on gelatine or agar- 

 agar ; in other words, such nitrogenous substances as these are 

 not affected by these organisms, and therefore such substances 

 are not directly available for plant food. But it has lately been 

 shown that if along with the nitrifying bacteria another is added 

 which is capable of breaking up the gelatine or agar-agar with 

 formation of ammonia, then the former grow and flourish, and 

 these substances then break down completely, and yield their 

 nitrogen ultimately in the form of nitrates ; i.e., in the form suit- 



