August 20, 1886.] 



SCIE^NCJi!. 



161 



The exportation of agricultural products, be- 

 comes, therefore, a slow but certain method of 

 securing soil exhaustion ; and this accounts for 

 the fact that countries — or those portions of 

 countries wh'ch are devoted to almost exclusive 

 agricultural pursuits, thus causing a continuous 

 exportation of agricultiu-al products — become the 

 homes, not of the richest, but of the poorest com- 

 munities. 



It would be useless to deny in this connection 

 that our own countiy, with a soil enriched by cen- 

 turies of accumulated nitrogen, has grown rich 

 from its agricultural exports. But when the last 

 of our virgin soil shall have been placed under 

 cultivation, a continuous stream of such exports 

 will certainly impoverish the nation, and reduce 

 all who practise such agriculture to the condition 

 which has already been reached by those who 

 have for years grown tobacco, corn, cotton, and 

 wheat on the same soil, and sold the products 

 without paying back to the field the percentage of 

 profits which was its due. On the other hand, 

 the farmer who is fortunate enough to be permit- 

 ted to patronize the home market, who sells his 

 maize and takes home a load of manure, adds not 

 only to the plethora of his purse, but also to the 

 fertility of his soil. 



Thus, in the light of agricultural chemistry, we 

 see clearly the deep scientific basis of the teachings 

 of political economy which show the value of the 

 home market. While, therefore, the statement 

 that the chief factor in the prosperity of a country 

 is its agriculture, remains in every sense true, yet, 

 from the data discussed, it as readily appears 

 that agricultural prosperity is most intimately 

 connected with the advancement of every other 

 industry. Agricultural chemistry teaches the 

 farmer to welcome the furnace and the mill, for 

 in their proximity he secures a sure return to his 

 fields of the plant-foods removed in his crops. 



We have seen by the foregoing discussion, that, 

 without any artificial additions, the soil, exclud- 

 ing the subsoil, contains enough of the two most 

 important and valuable mineral constituents of 

 plants to produce an average crop annually for 

 two hundred and fifty years. In point of fact, 

 however, the impoverishment of the soil takes 

 place at a much slower rate than this theory 

 would indicate. It would indeed be a sorry 

 thought to consider that in a quarter of a millen- 

 nium more the agricultural area of the earth 

 .would be incapable of producing further yields. 

 Doubtless much of this reserve food is brought 

 from the subsoil ; and, if it be possible for the 

 subterraneous stores of these materials to grad- 

 ually work their way surfacewards, even the re- 

 mote future need not fear a dearth of them. 



There is also a certain conservatism in crops, a 

 vegetable ' good breeding,' which prevents the 

 growing plant from taking all the food in sight. 

 As long as there is abundance, the plant is a 

 hearty eater ; but, when the visible quantity of 

 food falls to a certain minimum, it remains for a 

 long time without any rapid diminution. This 

 fact is well illustrated in the experiments of Lawes 

 and Gilbert at Eothamstead, where wheat was 

 grown on the same unmanured field for forty 

 years in succession. 



Professor Wiley then passed to a discussion of 

 the sources of supply of nitrogen used as plant-food, 

 and, after giving an extended account of the most 

 recent researches, summed up the results as fol- 

 lows: — 



1. The combined nitrogen, which is the product 

 of vegetable and organic life, forms the chief 

 source of nitrogen for the growing plant. 



2. Before it is assunilable by the plant it under- 

 goes a process of oxidation, which is due solely to 

 a living organism. 



3. The nitrates thus formed are absorbed by the 

 plant, and the alliuminoids of the new growth are 

 formed from the nitric nitrogen by a process of re- 

 duction. The nitrates themselves are subject to 

 the action of a ferment, by which a deoxidation 

 takes place, and free nitrogen and nitrous oxide 

 are evolved. 



4. The diminution in the quantity of available 

 nitrogen thus supplied is restored by the fixation 

 of free nitrogen by the action of organisms in the 

 soil, or by the oxidation of free nitrogen by the 

 interior cells of the plant acting in a manner anal- 

 ogous to the nitric ferment in the soil ; or by the 

 oxidation of free nitrogen by electrical discharges 

 or by combustion. 



5. The quantity of combined nitrogen brought 

 to the soil and growing plant 'by the rain-water 

 and the atmosphere, arising from the last two 

 phenomena, is an inconsiderable amount, when, 

 compared with the whole weight required by the 

 crop. 



Since, with a proper economy, the natural sup- 

 plies of potash and phosphoric acid may be made 

 to do duty over and over again, and last indefi- 

 nitely, the economist, who looks to the welfare of 

 the future, need have no fear of the failure of these 

 resourches of the growing plant. Indeed, it may 

 be said that the available quantities of them may 

 be increased by a wise practice of agricultm-e 

 based on the teachings of agricultural chemistry. 



But with the increase of population comes an 

 increased demand for food, and, therefore, the 

 stores of available nitrogen must be enlarged to 

 supply the demands of the increased agricultural 

 product. It is certain that, with new analytical 



