476 OIIGANOLOGY. 



on the estate must be reduced as food by at least one half. Boussingault 

 places the yearly account of dry organic products contained in the ma- 

 nure in contrast with the products obtained from the soil, during a 

 period of twenty-one years, and finds the proportions are as 33 to 124, 

 so that it would be constantly necessary to replace three-fourths of the 

 humus present, and thus every soil within a short time must be per- 

 fectly exhausted of organic matters. According to Sir H. Davy, 



Organic Matters 

 and Salts. 



Good soil for the growth of Hops contains . 8*0 per cent. 



Good soil for Turnips ..... 0*6 



Very good soil for Wheat . . . . . 4'4 

 Extraordinarily fruitful soil . . . . 2-8 



Good soil 1-4 



Excellent Wheat soil 127 



It is thus very clear that the fruitfulness of the soil does not stand in 

 any relation to its contents of organic substances, but that it appears to 

 depend, on the contrary, on the nature of the plants cultivated and the 

 tillage of the soil. 



But we are enabled to take quite a different view of the culture of 

 plants, if we do not confine ourselves to the little spot of earth from 

 which our profound agricultural manuals are supplied with material. 

 Loudon gives a view of the kinds of agriculture according to the follow- 

 ing scheme : 



1. Agriculture with exclusive irrigation, extending to 35 on each 

 side of the equator. 



2. Agriculture with irrigation and manuring, extending from 35 to 

 45 N. and S. lat. 



3. Agriculture with draining and manuring, from 45 to 67 lat. 



As the last zone alone embraces any considerable surface of the earth 

 in the northern hemisphere, and as local circumstances, both in the second 

 and third, according to the nature of the plant, determine the use of 

 manure or irrigation, it may be advanced, without fear of contradiction, 

 that generally three-fourths of the agriculture of the surface of the earth 

 is carried on without the aid of organic manures, and that the produce 

 in such districts is much greater than where it is carried on in unfavour- 

 able regions by the aid of manures. Unfortunately travellers have 

 given us much too little information of the various ways in which agri- 

 culture is carried on in different lands. As plants that are cultivated 

 without manure we may name the Maize, Rice, Sugar-cane, Plantain, 

 Banana, Manioc, Yams, Coffee, &c. ; as regions in which no organic 

 manures are employed, and in which irrigation alone is employed in 

 the culture of plants, we may mention Central Russia, in Spain the 

 district of Malaga, Arabia, Hindostan, Birman, Java, Ceylon, Malacca, 

 Siam, Cochinchina, Tonquin, a part of Japan and China, Van Diemen's 

 Land, a part of New Holland, Polynesia, Abyssinia, Egypt, Morocco, 

 Cape of Good Hope, Madagascar, Madeira, Chili, Mexico, the Brazils, a 

 part of Canada and of North America. In a word, the way in which 

 the experience of agriculture has been employed for a theory of the 

 nutrition of plants, reminds one very much of the contracted horizon of 

 a small town, Philistine. 



In accordance with these views, then, we maintain the right to reject, 

 without inquiry, every theory of vegetable nutrition which does not put 



