On Agricultural Chemistry. 



29 



it is not likely to be deficient in carbon or in mineral matter ; 

 while the Turnip, on the other hand, will not be provided with 

 the due quantity of carbon independently of a coincident and 

 frequently sufficient supply of nitrogen. And it is in this 

 conversion into useful food for stock by the Root crop of the 

 carbonaceous matter of our straw, which, after it has served 

 as litter, would, beyond this, be a comparat'vely useless refuse 

 of our grain crops, that phosphoric acid is found to be a very 

 active agent; whilst of the nitrogen stored up in the growth 

 of the root crop, a much larger proportion than of the carbon 

 remains in the excrements of the animals, and serves in its turn 

 for the growth of the succeeding cereal grain ; and hence is seen 

 a mutual reliance between these two important crops of rotation. 

 But to the influence of phosphoric acid upon the turnip crop we 

 shall recur again presently. 



But there is another point in connexion with the great demand 

 made by the wheat plant upon nitrogen supplied to the soil, to 

 which we wish to draw particular attention. 



Thus, among from two to three hundred experiments with 

 ammoniacal manures, we have in no single instance recovered in 

 the increase the amount of nitrogen provided in the manure ; 

 and this fact is perfectly consistent with the amounts of produce 

 found, in the experience of the farmer, to be obtained by the use 

 of Peruvian guano and other nitrogenous manures. Part of this 

 result is doubtless due to the limited range of the roots of the 

 plant in relation to the distribution of the manure in the soil ; 

 but much of it is materially dependent on a definite expenditure, 

 so to speak, of nitrogen, which is taken up by the roots of the 

 plant and given off by its leaves to the atmosphere in the exercise 

 of the functional actions of its growth. 



De Saussure, Daubeny, and Draper have found that nitro- 

 gen was really thus given off during the growth of certain plants ; 

 but in a practical point of view the question still arises whether 

 this is uniform with all the different plants which enter into a 

 rotation. 



In relation to this subject we have ourselves, during the last 

 tw^o years, undertaken a series of experiments, in the hope of 

 sooner or later elucidating this truly interesting and important 

 subject. We cannot here enter into a consideration of the results 

 which have been thus obtained, but we may briefly indicate a 

 probable conclusion to which the experiments would seem to lead, 

 the results of a preliminary series of which have already been 

 published in the Journal of the Horticultural Society, for January 

 1850. Thus we have found, that whilst for a given quantity of 

 vrater passed through the plant during its growth the amount of 

 72C?i-nitrogenous substances fixed in it is, within somewhat narrow 



