THE FARMER'S MAGAZINE. 



Ill 



THE FOOD OF PLANTS. 



The ancients inquired, by very laborious researches, 

 into the nature of vegetable growth ; but the results 

 were very unsatisfactory. The transmutation of air into 

 the different bodies was held as an undoubted truth by 

 Epicurus and Pythagoras; and Lucretius, in the beau- 

 tiful poem, " De Rerum Natura," affirms the con- 

 stant change of air into other substances which are re- 

 solved into air, and which is again decomposed into 

 bodies by a continual and never-ceasing rotation. 

 Anaximenes also believed that all bodies wore formed of 

 air, or of aerial matters. Among the moderns, Law- 

 rence contended for fire, Helmont for water, Bradley for 

 air, and others for earth and nitre ; and this uncer- 

 tainty continued till more recent discoveries found that 

 liquids, carbonaceous, gaseous, and other substances 

 entered into the food of plants, and that water and air 

 are compound substances — the former consisting of two 

 elastic fluids or gases, viz., inflammable air or hydro- 

 gen, and vital gas or oxygen, or the oxide of hydro- 

 gen, and in weight 1+8 of oxygen; and the latter of 

 two gases, oxygen and azote, and small quantities of 

 aqueous vapour and of carbonic-acid gas — this last sub- 

 stance being itself a compound elastic fluid, consisting 

 of charcoal dissolved in oxygen. Tull thought that the 

 earth reduced to very minute particles supplied the 

 nourishment to vegetables, by attracting much moisture 

 in that comminuted state ; and that manures only 

 acted mechanically in improving the texture and in 

 crumbling the particles, and thus increasing the power 

 of attraction. Duhamel adopted these opinions, and 

 thought manures unnecessary ; but he lived long 

 enough to abandon that notion, and he finally 

 concluded that no single material composed the 

 food of plants. Succeeding philosophers have made 

 many experiments on the growth of vegetables in 

 different situations, in light and in darkness, and placed 

 in substances of diflerent qualities ; and the results 

 satisfied them that light and atmospheric air have 

 great influence, and that water is essentially necessary 

 to organized bodies, as without it no circulation of juices 

 can be cai-ried on, though it be only reckoned a vehicle, 

 and not to constitute any part of the food itself. In- 

 genhousz contended for atmospheric air by many very 

 ingenious reasonings, which have not yet been clearly 

 proved or understood. Hassenfratz argued for carbon 

 or charcoal being the chief food of plants, and derived 

 from the soil by the roots, supplied to them in a state 

 of solution or suspension from the brown sediment of 

 dung after evaporation. This opinion was adopted by 

 Kirwan, with the difierence of supposing that plants 

 derived carbon from the air by the act of vegetation, as 

 carbonic acid gas is easily resolved into its two ingre- 

 dients, oxygen and carbon. But common air lias been 

 shown to contain only a thousandth part of its bulk of 

 carbonic acid gas, or, according to Lavoisier, none at all; I 



and carbon forms only one-fourth part of the fixed air it- 

 self. And it is doubtful if the brown mud ofdungremain- 

 ing after evaporation can be reckoned real coal without 

 undergoing the action of fire ; it may rather be called 

 an extract, as it may be again diffused through water, 

 or dissolved as it was before the evaporation. Saussure 

 would lead us to believe that plants obtain their earths 

 from the soil ; for beans, supported by distilled water, 

 yielded only one-third of the quantity of ashes afforded 

 by those grown in the soil ; while those fed by rain- 

 water gave little more than one-half of the latter 

 quantity. 



Thirty-two ounces of dry corn contained earths and 

 metallic oxides as under — 



Wheat. Rye. Barley. Oats, 



Carbonate of lime 12-6 13-4 24-8 3375 



Silica 13-2 156 667 1442 



Carbonate of magnesia ... . 13-4 14-2 25-3 339 



Alumina 0-6 1'4 4*2 4-5 



Oxide of manganese 5'0 32 67 6-95 



Oxideofiron 2-5 0.9 3-8 45 



One hundred parts of ashes lixiviated gave as 

 under — 



Silex, Calx and Argil. 

 Muriatic. 



Wheat 48 37 15 



Barley 69 16 15 



Oats 68 26 6 



Bear or here 65 25 10 



Eye 63 21 16 



Potatoes 4 66 30 



Red clover 37 33 30 



Schroeder seems to prove that a part of the earths 

 must be dei'ived from vegetation, even where plants are 

 deprived of any opportunity of deriving fixed princi- 

 ciples from the soils where they grow. He planted 

 vegetables in sulphur and in the oxides of antimony 

 and zinc, containing no earthy matter, and placed them 

 in boxes, with free access of light and air, with dust and 

 rain excluded, and fed them with distilled water. He 

 found that the plants contained more earthy matter 

 than the seed from which they grew, and which he had 

 previously analyzed and ascertained the constituent 

 parts. Plants growing in distilled water, and with free 

 access of light and air, nearly doubled the portion of 

 carbon they originally contained ; but with little share 

 of light, it was diminished from the latter quantity : 

 and hence the plants must have derived nourishment 

 from the air. But as they never perfect seeds, and soon 

 decay, it is evident that air and water alone cannot 

 support healthy and productive vegetation. Plants 

 draw earthy matter from soils where no earths of that 

 kind exist ; as much as 65 per cent, of lime has been 

 found in plants, of which substance no traces could be 

 found in the ground ; and silica also, though none ex- 

 isted where the plants grew. 



It has been found, by experiment, that plants do not 

 absorb solutions of saline substances indiscriminately ; 



I 



