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lias when exposed in a favourable environment. It is true that the pure 

 cultures which the laboratory would afford would be of little avail if 

 limited to their own activity, and it is alone in the possibilitv of their 

 almost illimitable development that their fertilising effects may be 

 secured. 



NUMBERS AND KINDS OF NITRIFYING ORGANISMS. 



In regard to the numbers and kinds of organisms, which take part in 

 the evidence of nitrogenous bodies, our knowledge is limited. It has 

 already been noted that a great many species take part in the production 

 of ammonia. The purely nitrous and nitric ferments seem to be of a more 

 limited character, but it must not be forgotten that scarcely a beginning 

 has been made in the investigation of these bodies, and it is entirely 

 probable that the great differences in their nature will be established. 

 It is not at all likely, for instance, that a nitrifying organism such as 

 exerts its activity in an ordinary soil under ordinary conditions would 

 belong to a species which was capable of development and work in an 

 entirely different medium. There are in the arid regions indubitable 

 evidence of strong nitrification in the presence of highly alkaline salts. 

 While it is true that a slight alkalinity favours the ordinary form of 

 nitrifying activity, it is likewise certain that such organisms would be 

 practically paralysed if subjected to the alkaline environment of the arid 

 plains. It is therefore highly desirable that the investigation of these 

 organisms be pushed to the widest extent, not only for the scientific 

 value of the investigation, but also for its practical utility in scientific 

 farming. This is one of the objects kept in view in the investigation 

 which the department has undertaken in respect of the extent and cha- 

 racter of the nitrifying ferments in the typical soils of the United 

 States. 



FERMENTS OXIDIZING FREE NITROGEN. 



In the preceding paragraphs the attention of the reader has been 

 briefly called to the action of those species of ferments which attack 

 nitrogen in some of its forms of combination. Since nitrogenous food is 

 the most expensive form of nutriment which the plant consumes, it is a 

 matter of grave importance to agriculture to know the full extent of the 

 supply of this costly substance. It is evident that the continued action 

 of nitrifying ferments finally tends to exhaust the store of this sub- 

 stance which has been provided in the soil. The quantities of oxidized 

 nitrogen produced by electric discharges in the air and by other me- 

 teorological phenomena, and which are brought to the soil in rain waters 

 are of considerable magnitude, but lack much of supplying the ordinary 

 wastage to which the stores of soil nitrogen are subjected. Even with 

 the happiest combination of circumstances, it is not difficult to see in 

 what way the available stores of nitrogen could be diminished to a point 

 threatening the proper sustenance of plants, and thus diminishing the 

 necessary supplies of human food. The examination of the drainage 

 waters which come from a fertile field in full cultivation is sufficient to 

 convince the most sceptical of the fact that the growing crop does not 

 by any means absorb all of the products of the activity of the nitrifying 

 ferments, Nitric acid and its compounds, the nitrates, are exceedingly so- 

 luble in water, and for this reason any unappropriated stores of them in the 

 soil are easily removed by heavy downpours of rain. Happily the living 



