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circumstanced. Thus when indigo or tobacco is grown, the 

 object is to obtain the greatest possible development of the co- 

 louring or of the narcotic principle. For this purpose, elements 

 are necessary of which the soil is thereby deprived, but the 

 impoverishing of the soil is paid for, by its materials being 

 sold as the valuable portion of the plant. In such cases, 

 therefore, to sustain the fertility of the soil, a continued sup- 

 ply, from external sources, of the materials which the plants 

 take up is required. The farmer must supply in the manure 

 the elements which he sends to market in the grown plants. 

 Dr. Kane then proceeded to point out that this principle 

 was limited as to certain classes of plants, by the fact, now 

 clearly established by the concurrent investigations of vege- 

 table physiologists and of chemists, that certain vegetable 

 substances, and those of high importance to mankind, were 

 not formed of materials abstracted from the soil, but were 

 produced by the vital action of the plant upon the consti- 

 tuents of the atmosphere. This class of bodies he charac- 

 terized as being constituted, generally, of carbon, united with 

 hydrogen and oxygen in the proportions which form water. 

 The carbonic acid of the atmosphere, with the watery vapour 

 constantly existing in it, supplies the elements of sugar, gum, 

 starch, and ligneous fibre, and the oxygen of the carbonic 

 acid, evolved by the vital action of the plants, tends, as it is 

 well known, to ameliorate the air we breathe. When, there- 

 fore, we take the sugar, or the woody fibre of a plant, we 

 have a material, formed, as to its elements, independent of 

 the soil. For its formation is required a plant in healthy 

 vegetation, and for the plant to be in healthy vegetation, it 

 may require to abstract from the soil various materials, so that 

 the crop may actually be of a highly exhausting nature. Slill 

 those materials do not go to the sugar or to the fibre; they 

 exist in other portions of the plant; and if the sugar or fibre 

 be tlie valuable portion of the crop, as in reality usually oc- 

 curs, the elements which render its production costly are re- 

 jected, and let to waste; they do not subserve any future 



