AGRICULTURAL CHEMIS'iRY. 



son, cannot live unless supplied with cer- 

 tain metallic compounds. 



If we knew with certainty that there ex- 

 isted a substance capable alone of nour- 

 ishing a plant and of bringing it to maturity, 

 we might be led to a knowledge of the con- 

 ditions necessary to the life of all plants, by 

 studying its characters and composition. If 

 humus were such a substance, it would 

 have precisely the same value as the only 

 single food which nature has produced for 

 animal organization, namely, milk (Prout.) 

 The constituents of milk are cheese or 

 caseine, a compound containing nitrogen in 

 large proportion ; butter, in which hydrogen 

 abounds j and sugar of milk, a substance 

 with a large quantity of hydrogen and oxy- 

 gen in the same proportion as in water. It 

 also contains in solution, lactate of soda, 

 phosphate of lime, and common salt; and a 

 peculiar aromatic product exists in the but- 

 ter, called butyric acid. The knowledge of 

 the composition of milk is a key to the con- 

 ditions necessary for the purposes of nutri- 

 tion of all animals. 



All substances which are adequate to the 

 nourishment of animals contain those ma- 

 terials united, though not always in the 

 same form ; nor can any one be wanting for 

 a certain space of time, without a marked 

 effect on the health being produced. The 

 employment of a substance as food presup- 

 poses a knowledge of its capacity of assimi- 

 lation, and of the conditions under which 

 this takes place. 



A carnivorous animal dies in the vacuum 

 of an air pump, even though supplied with 

 a superabundance of food j it dies in the air, 

 if the demands of its stomach are not satis- 

 fied ; and it dies in pure oxygen gas, how- 

 ever lavishly nourishment be given to it. Is 

 it hence to be concluded, that neither flesh, 

 nor air, nor oxygen, is fitted to support life? 

 Certainly not. 



Prom the pedestal of the Trajan column 

 at Rome we might chisel out each single 

 piece of stone, if upon the extraction of the 

 second we replaced the first. But could we 

 conclude from this that the column was sus- 

 pended in the air, and not supported by a 

 single piece of its foundation ? Assuredly 

 not. Yet the strongest proof would have 

 been given that each portion of the pedestal 

 could be removed, without the downfall of 

 the column. 



Animal and vegetable physiologists,, how- 

 ever, come to such conclusions with re- 

 spect to the process of assimilation. They 

 institute experiments, without being ac- 

 quainted with the circumstances necessary 

 for the continuance of life with the quali- 

 ties and proper nutriment of the animal or 

 plant on which they operate or with the 

 nature and chemical constitution of its 

 organs. These experiments are considered 

 by them as convincing proofs, while they 

 are fitted only to awaken pity. 



Is it possible to bring a plant to maturity i 

 by means of carbonic acid and water, with- I 



out the aid of some substance con tuuimg ni- 

 trogen, which is an essential constituent oi 

 the sap, and indispensable for its produc- 

 tion ? Must the plant not die, however 

 abundant the supply of carbonic acid may 

 be, as soon as the first small leaves have 

 exhausted the nitrogen contained in the 

 seeds 1 



Can a plant be expected to grow in Car- 

 rara marble, even when an azotised sub- 

 stance is supplied to it, if the marble be 

 sprinkled with an aqueous solution of car- 

 bonic acid, which dissolves the lime and 

 forms bicarbonate of lime ? A plant of the 

 family of the Plumbaginece, upon the leaves 

 of which fine hornlike, or scaly processes 

 of crystallised carbonate of lime are formed, 

 might, perhaps, attain maturity under such 

 circumstances; but these experiments are 

 only sufficient to prove, that cresses, gourds, 

 and baisamines, cannot be nourished by 

 bicarbonate of lime, in the absence of mat- 

 ter containing nitrogen. We may, indeed, 

 conclude, that the salt of lime acts as a 

 poison, since the developement of plants 

 will advance farther in pure water, when 

 lime and carbonic acid are not used. 



Moist flowers of sulphur attract oxygen 

 from the atmosphere, and become acid. Is 

 it possible that a plant can grow and flourish 

 in presence of free sulphuric acid, with no 

 other nourishment than carbonic acid ? It is 

 true, the quantity of sulphuric acid formed 

 thus in hours, or in days, may be small, but 

 the property of each particle of the sulphur 

 to absorb oxygen and retain it, is present 

 every moment. 



When it is known that piants require 

 moisture, carbonic acid, and air, should we 

 choose as the soil for experiments on their 

 growth, sulphate of barytes, which, from its 

 nature and specific gravity, completely pre- 

 vents the access of air? 



All these experiments are valueless for the 

 decision of any question. It is absurd to 

 take for them any soil, at mere hazard, as 

 long as we are ignorant of the functions 

 performed in plants by those inorganic sub- 

 stances which are apparently foreign to 

 them. It is quite impossible to mature a 

 plant of the family of the Graminece, or of 

 the Equisctacece, the solid framework of 

 which contains silicate of potash, without 

 silicic acid and potash, or a plant of the ge- 

 nus Oxalis without potash, or saline plants 

 such as the saltworts (Salsola and Salicorma) 

 without chloride of sodium, or at least some 

 salt of similar properties. All seeds of the 

 Graminece contain phosphate of magnesia ; 

 the solid parts of the roots of the althcea con- 

 tain more phosphate of lime than woody fibre. 

 Are these substances merely accidentally 

 present ? A plant should not be chosen for 

 experiment, when the matter which it re 

 quires for its assimilation is not well known, 



What value, now, can be attached to ex- 

 periments in which all those matters which 

 a plant requires in the process of assimila- 

 tion, besides its mere nutriment, 1 ave been 



