58 



ON INCREASING THE GROWTH 



add here another remark. In our previous declara- 

 tion, true as it is, that nitrogen is the most valuable 

 ingredient of such substances as are used for manure, 

 we do not intend to affirm that their remaining con- 

 stituents — for example, potash, lime, phosphoric 

 acid, etc. — are less important than nitrogen to the 

 nourishment of plants. In this respect, indeed, all 

 the separate substances, whether they be dear or 

 cheap, scarce or universally diffused, which plants 

 require for their development and complete forma- 

 tion, must be regarded as equally important. 



The matter, however, assumes a different shape if 

 the value in money^ which these several ingredients 

 may cost the farmer, is taken as the standard when 

 the question is proposed, How might the farmer 

 be able to procure this or that constituent in an- 

 other manner at the cheapest price ? From this 

 point of view, very different values are assigned to 

 these separate elements, and nitrogen must indisput- 

 ably be pronounced by far the dearest and most cost- 

 ly amongst them. Upon this subject more precise 

 information is contained in Chapter VII. 



2. Substances forming humus, or organic elements. 

 By these appellations are to be understood those 

 constituents of manure which are composed of car- 

 bon, oxygen, and hydrogen, and which form the bulk 

 of ordinary stable-manure. Without greatly erring, 

 vegetable fibre, the most generally diffused proximate 

 constituent of the vegetable kingdom, may be re- 

 garded as the exclusive producer of humus ; inas- 



