AS ILLUSTRATED BY THE POTATO MUERAIN. 187 



opposed to one another. This does not, however, always take 

 place in such a manner that the matter in solution is taken up in 

 the same proportion in wliich it is present in the solvent water ; 

 nevertheless, in the case of the fluids which most frequently 

 occur, and the constituents usually dissolved in the water present 

 in the ground, the limit is so wide that the quantities extend far 

 beyond the necessities of a plant. 



According to these premises, the point is not merely that the 

 matters, which the plant must find as nutriment in the ground, 

 must be generally present, but more especially that they must 

 exist in the ground in the same, or nearly the same, proportions 

 as they do in the plant when healthy. Every abnormal propor- 

 tion will compel the plant to take a nutriment unsuitable to its 

 nature, the consequence of which will be that the chemical pro- 

 cess by which the organic matters are formed will be modified, 

 and a relation of these matters induced which recedes from that 

 of a plant in its normal condition; and cases may arise in which 

 matters which ought to be present in the jjlant may entirely fail, 

 while other analogues may take their place and altogether new 

 compounds be formed. Thus in the cases adduced by Liebig, 

 where the requisite inorganic bases or acids fail, the plant forms 

 organic bases or acids which supply the place of those which are 

 wanting. 



In every plant a certain normal proportion is found between 

 the combinations of protein and those of dextrin. A deviation 

 from tliese by no means necessarily infers the destruction of the 

 plant, for in our agricultural plants the very point we aim at is 

 the regular predominance of some particular constituent. We 

 see, for instance, how extremely different the proportions may be 

 in the seeds of our cultivated wheat without the existence of the 

 plant being endangered. But it is equally notorious how many 

 diseases it is exposed to, as bunt, rust, mildew, &c. ; and every 

 intelligent cultivator agrees that seed-corn should be selected 

 from the most barren land, since that produces the healthiest and 

 most vigorous plant, and gives the surest and richest return. 



Liebig has strived very cleverly to prove the intimate con- 

 nexion which makes the formation of dextrinous matters de- 

 pendent on the presence of alkaline salts : he and Boussingault 

 have shown in their analyses in what a close reciprocity the 

 protein matters seem to stand to the phosphates. If these doc- 

 trines are not free from objection, yet thus much is certain — 

 that the presence and the proportion of phosphoric acid to the 

 alkalies stands in the closest relation to the formation and the 

 proportions of the combinations both of protein and dextrin. 



Now by means of manure which consists of animal excrements, 

 phosphates are continually carried to the soil in greater quan- 



