4S 



AGRICULTURAL CHEMISTRY. 



nured with strong animal manure, although 

 then the number of cells increases, the po- 

 tatoes acquiring in the first case a mealy, in 

 the second a soapy, consistence. Beet-roots, 

 taken from a barren, sandy soil, contain a 

 maximum of sugar, and no arnmoniacal 

 salts; and the Teltowa parsnep loses its 

 mealy state in a manured land, because there 

 all the circumstances necessary for the for- 

 mation of cells are united.* 



An abnormal production of certain com- 

 ponent parts of plants presupposes a power 

 and capability of assimilation to which the 

 most powerful chemical action cannot be 

 compared. The best idea of it may be 

 formed by considering that it surpasses in 

 power the strongest galvanic battery, with 

 which we are not able to separate the oxy- 

 gen from carbonic acid. The affinity of 

 chlorine for hydrogen, and its power to de- 

 compose vnater under the influence of light 

 and set at liberty its oxygen, cannot be con- 

 sidered as at all equalling the power and 

 energy with which a leaf separated from a 

 plant decomposes the carbonic acid which 

 it absorbs. 



The common opinion, that only the direct 

 solar rays can effect the decomposition of 

 carbonic acid in the leaves of plants, and 

 that reflected or diffused light does not pos- 

 sess this property, is wholly an error, for 

 exactly the same constituents are generated 

 in a number of plants, whether the direct 

 rays of the sun fall upon them, or whether 

 they grow in the shade. They require light, 

 and indeed sun-light, but it is not necessary 

 that the direct rays of the sun reach them. 

 Their functions certainly proceed with 

 greater intensity and rapidity in sunshine 

 than in the diffused light of day; but there 

 is nothing more in this than the similar 

 action which light exercises on ordinary 

 chemical combinations; it merely accelerates 

 in a greater or less degree the action already 

 subsisting. 



Thus chlorine and hydrogen combining 

 form muriatic acid. This combination is 

 effected in a few hours in common daylight, 

 but it ensues instantly, with a violent ex- 

 plosion, under exposure to the direct solar 

 rays, whilst not the slightest change in the 

 two gases takes place in perfect darkness. 

 When the liquid hydrocarburet of chlorine, 

 resulting from the union of the olefiant gas 

 of the associated Dutch chemists with chlo- 

 rine, is exposed in a vessel with chlorine 

 gas to the direct solar rays, chloride of car- 

 bon is immediately produced ; but the same 

 compound can be obtained with equal faci- 

 lity in the diffused light of day, a longer time 

 only being required. When this experiment 

 is performed in the way first mentioned, two 



* Children fed upon arrow-root, salep, or in- 

 deed any kind of amylaceous food, which does 

 not contain ingredients fined for the formation of 

 bones and muscles, become fat, and acquire much 

 embonpoint ; their limbs appear full, but they do 

 not acquire strength, nor are their organs pro- 

 perly developed. 



'products only are observed (muri&Mc acid 

 land perchloride of carbon); whilst by the 

 j latter method a class of intermediate bodies 

 I are produced, in which the quantity of chlo- 

 rine constantly augments, until at last the 

 whoie liquid hydrocarburet of chlorine is 

 converted into the same two products as in 

 the first case. Here, also, not the slightest 

 trace of decomposition takes place in the 

 dark. Nitric acid is decomposed in common 

 daylight into oxygen, and peroxide of nitro- 

 gen ; and chloride of silver becomes black 

 in the diffused light of day, as well as in the 

 direct solar rays ; in short, all actions of a 

 similar kind proceed in the same way in dif- 

 fused light as well as in the solar light, the 

 only difference consisting in the time in 

 which they are effected. It cannot be other- 

 wise in plants, for the mode of their nutri- 

 ment is the same in all, and their component 

 substances afford proof that their food has 

 suffered absolutely the same change, whether 

 they grow in the sunshine or in the shade. 



All the carbonic acid, therefore, which 

 we supply to a plant will undergo a trans- 

 formation, provided its quantity be not 

 greater than can be decomposed by the 

 leaves. We know that an excess of car- 

 bonic acid kills plants, but we know also 

 that nitrogen to a certain degree is not essen- 

 tial for the decomposition of carbonic acid. 

 All the experiments hitherto instituted prove, 

 that fresh leaves placed in water impregnated 

 with carbonic acid, and exposed to the in- 

 fluence of solar light, emit oxygen gas, 

 whilst the carbonic acid disappears. Now 

 in these experiments no nitrogen is supplied 

 at the same time with the carbonic acid ; 

 hence no other conclusion can be drawn 

 from them than that nitrogen is not neces- 

 sary for the decomposition of carbonic acid, 

 for the exercise, therefore, of one of the 

 functions of plants. And yet the presence 

 of a substance containing this element ap- 

 pears to be indispensable for the assimilation 

 of the products newly formed by the decom- 

 position of the carbonic acid, and their con- 

 sequent adaptation for entering into the 

 composition of the different organs. 



The carbon abstracted from the carbonic 

 acid acquires in the leaves a new form, in 

 which it is soluble and transferable to all 

 parts of the plant. In this new form the 

 carbon aids in constituting several new pro- 

 ducts ; these are named sugar when they 

 possess a sweet taste, gum or mucilage 

 when tasteless, and excrementitious matters 

 when expelled by the roots. 



Hence it is evident that the quantity and 

 quality of the substances generated by the 

 vital processes of a plant will vary accord- 

 ing to the proportion of the different kinds 

 of food with which it is supplied. The de- 

 velopement of every part of a plant in a 

 free and uncultivated state depends on me 

 amount and nature of the food afforded to it 

 by the spot on which it grows. A plant is 

 developed on the most sterile and unfruitful 

 soil as well as on the most luxuriant and 



