32 



On Agricultural Chemistry. 



consumption of the nitrogenous bodies derived through the roots, 

 connected with the fixation and elaboration of certain constituents 

 of plants, and that this is greater or less according to the sources 

 or the exact composition or state of elaboration of the products, and 

 an 'important step will be gained towards a clearer conception of 

 the principles involved in the alternation in a course of cropping, 

 of plants of varying products and habits of growth. The fallacy, 

 too, of the theory which would supply to plants a manure, 

 founded on a knowledge of the percentage composition alone, 

 whether of their ashes or of their organic substance, will at once 

 be obvious. Nay, the converse of the axiom herein implied is 

 more nearly true, at least in some important cases ; for, as we 

 have elsewhere asserted, with regard to the Wheat and Bean 

 plants for example, the former, that is the Wheat, as compared 

 with the latter, is characterized by a low percentage of nitrogen 

 and a relatively high percentage of carbon ; but all experience 

 and the tendency of all our results is to show, that the low 

 nitrogenized Wheat crop requires for its luxuriant growth an 

 abundant supply of nitrogen by manure, and that Avith this it is 

 'practically independent of supplied carbon ; whilst the highly 

 nitrogenous Leguminous plant is, other things being equal, by 

 no means strikingly and characteristically benefited by nitro- 

 genous manures. Were it otherwise, where would be the sub- 

 serviency of the leguminous plants grown in rotation with grain ? 

 We had, indeed, at one time supposed that clover was greatly 

 dependent on an artificial provision of nitrogen, but this view is 

 not favoured by further investigation ; whilst with it, as well as 

 with those leguminous plants valued in agriculture for their 

 seeds, which are known practically to occupy a peculiar sphere 

 when grown in alternation with the cereal grains, a mineral, and 

 especially an alkaline manure, seems to be more prominently 

 indicated. Indeed, it is to the falloio crops generally, or those 

 which are grown in alternation with grain, that direct mineral 

 manures are of essential service in enabling them to accumulate 

 stores from the atmosphere ; and in this sense indeed special 

 mineral manures may be said to be subservient to the increased 

 growth of grain. And, the effect of alkalies upon leguminous 

 plants, perhaps approaches more nearly to consistency with the 

 theory of Baron Liebig than any other fact which has come under 

 our observation, for the alkalies, which we have found to have a 

 very marked effect upon their increased growth, predominate 

 largely in their ashes. 



A beautiful illustration of the dependence for luxuriant growth 

 of one plant upon another of different habits, such as we have 

 shown above, may be found in the case of the "fairy rings," 

 where the fungus, by virtue of its extraordinary power of rapidly 



