On the Application of Manures. 



241 



smaller proportion than the rest ; and as all four, though present 

 in the soil, are also capable of volatilisation, or^, in other words, of 

 existing permanently in the atmosphere, it is quite open to con- 

 jecture^ whether plants obtain their elements from the one source 

 or from the other. 



The second class of constituents, comprehending substances 

 found in plants, which are incapable of being converted into va- 

 pour at such temperatures as they are exposed to in nature, con- 

 sists of the alkalies, earths, and metallic oxides, which by their 

 presence give firmness and solidity to the vegetable structure, and, 

 perhaps, by being interposed between the particles of living fibre, 

 may contribute in some other manner, as yet imperfectly under- 

 stood, to impart to it the properties it possesses.^ 



These of course cannot be conveyed through the medium of 

 the atmosphere, and hence the natural inference would seem to 

 be that they are derived from the soil in which the plants are 

 fixed. 



Yet this conclusion has been combated by many physiologists, 

 who allege that the above ingredients are found m plants even 

 when not present in the soil from, which thev proceed : and a 

 German chemist, Schrader, was honoured with a prize from the 

 Berlin Academy for having, as was thought, established this 

 position. 



Saussure, however, has shown that the same plant, when grovrn 

 upon a calcareous soil, contains more calcareous matter than it 

 does in a siliceous one, and T have myself instituted a series of expe- 

 riments which tend to demonstrate that, in proportion as vou de- 

 jmve a vegetable of all external means of obtaining its fixed con- 

 stituents, in that degree you dimmish the quantity of them which 

 it will contain; whence the natural inference would seem to be, 

 that if it were possible to intercept completely all the channels by 

 which it could derive these principles, none such Vv-ould be present 

 in its composition.! 



Thus the latest experiments confirm what both reason and 



* See Dr. Front's Treatise on the Stomach, &c,, introduction: and my In- 

 troduction to the Atomic Theory, p. 30. 



T The following were the results obtained in the experiments alluded to: 

 ■ — In Experiment 1. the object was merely to determine the variation in the 

 amount of sohd ingredients obtained, which might be referred to differences 

 m the soil or to different exposure to atmospheric inlluences. In Experiments 

 XL and III. it was also intended to ascertain, by watering the plants with a 

 solution of nitrate of strontian, whether the quality of the earthy ingre- 

 dients might be made to vary ad libitum according to the nature of those 

 presented to their roots in a soluble form. In the tabulated results given 

 underneath, the portion soluble in water represents the amount of car- 

 bonates — that soluble in acid the amount of sulphates and of phosphates 

 present. 



■Experiment 



