21 



from the atmosphere at probably not more than, if as much as, 

 5 pounds per aero per annum in the open country at Rothamsted. 



With records of the amounts of combined nitrogen contributed to 

 a given area in rain, we come to an end of all quantitative evidence 

 as to the amount of combined nitrogen available to the vegetation of 

 a given area from atmospheric sources. It will be seen how entirely 

 inadequate is the amount probably so available to supply the quanti- 

 ties yielded in different crops grown without nitrogenous manure, as 

 recorded in Tables I and III (pp. 8 and 14). 



It is true that the minor aqueous deposits from the atmosphere are 

 much richer in combined nitrogen than rain, and there can be no 

 doubt that there would bo more deposited within the pores of a given 

 area of soil than on an equal area of the non-porous even surface of a 

 rain-gauge. How much, however, of this might be available beyond 

 that determined in the collected aqueous deposits, existing evidence 

 does not afford the means of estimating with certainty. 



Other Supposed Sources of Combined Nitrogen. 



Further, it has been argued that, in the last stages of the decom- 

 position of organic matter in the soil, hydrogen is evolved, and that 

 this nascent hydrogen combines with the free nitrogen of the atmo- 

 sphere, and so forms ammonia. Again, it has been suggested that 

 ozone may be evolved in the oxidation of organic matter in the 

 soil, and that, uniting with free nitrogen, nitric acid would be pro- 

 duced. 



We have discussed these various possible supplies of combined 

 nitrogen to the soil from atmospheric sources on more than one occa- 

 sion ; and we have given our reasons for concluding that none of them 

 can be taken as accounting for the facts of growth. Incidentally, some 

 evidence will be given further on, confirming the conclusion that any 

 such supplies are limited and inadequate. 



But, if the supplies from the atmosphere to the soil itself are 

 inadequate, how about the direct supplies from the atmosphere to the 



plant ? 



One view which has been advocated is, that broad-leaved plants 

 have the power of taking up combined nitrogen from the atmosphere, 

 in a manner, or in a degree, not possessed by the narrow-leaved 

 gramineous plants. The only experiments that we are aware of, made 

 to determine whether plants can take up nitrogen by their leaves 

 from ammonia supplied to them in the ambient atmosphere, are those 

 of Adolph Mayer in Germany, and of Schlosing in France. Both 



