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XVIII. Abstract of a Memoir on the Chemical Constitution of 

 the Plants of Flax and Hemp, considered with relation to 

 the conditions of their Growth and Preparation. By Robert 

 Kane, M.D., fa,* 



TN those plants which are cultivated for the purpose of being 

 ultimately employed as food, it is found that certain con- 

 stituents are withdrawn from the soil, partly of an organic 

 and partly of an inorganic character, which give to the plant, 

 or to certain portions of it, the constitution that adapts it for 

 sustaining the animal organism. Thus nitrogen, alkalies, and 

 lastly, phosphates, &c, are found as components of plants, and 

 the value of the crop yielded by a certain surface of ground 

 is proportional, generally speaking, to the materials which the 

 crop has taken up. If, therefore, wheat or oats, or potatoes 

 exhaust a soil, the agriculturist does not suffer thereby, for he 

 is paid for the materials of which they have exhausted it, and 

 when he replaces that loss of material by fresh manure he but 

 invests a certain capital, to be delivered at a profit in the next 

 season. 



Many plants not employed as food, but ancillary to our 

 civilization as luxuries, or as utilized in the arts, are similarly 

 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 constitu- 

 ents of the atmosphere. This class of bodies he characterized 

 as being constituted, generally, of carbon, united with hy- 

 drogen and oxygen in the proportions which form water. The 

 carbonic acid of the atmosphere, with the watery vapour con- 

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

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



• Extracted from the Proceedings of the Royal Irish Academy, the 

 Memoir having been read December U, 1843. 



