AGRICULTURAL CHEMISTRY. 



Neither this emission of carbonic acid nor 

 the absorption of oxygen has any connection 

 with the process of assimilation; nor have 

 they the slightest relation to one another; 

 the one .s a purely mechanical, the other a 

 purely chemical process. A cotton wick, 

 inclosed in a lamp, which contains a liquid 

 saturated with carbonic acid, acts exactly in 

 the same manner as a living plant in the 

 night. Water and carbonic acid are sucked 

 up by capillary attraction, and both evapo- 

 rate from the exterior part of the wick. 



Plants which live in a soil containing hu- 

 mus exhale much more carbonic acid dur- 

 jig the night than those which grow in dry 

 situations ; they also yield more in rainy 

 than in dry weather. These facts point out 

 to us the cause of the numerous contradic- 

 tory observations, which have been made 

 with respect to the change impressed upon 

 the air by living plants, both in darkness 

 and in common daylight, but which are un- 

 worthy of consideration, as they do not 

 assist in the solution of the main question. 



There are other facts which prove in a de- 

 cisive manner that plants yield more oxygen 

 to the atmosphere than they extract from it; 

 these proofs, however, are to be drawn with 

 certainty only from plants which live under 

 water. 



When pools and ditches, the bottoms of 

 which are covered with growing plants, 

 freeze upon their surface in winter, so that 

 the water is completely excluded from the 

 atmosphere by a clear stratum of ice, small 

 bubbles of gas are observed to escape, con- 

 tinually, during the day, from the points of 

 the leaves and twigs. These bubbles are 

 seen most distinctly when the rays of the 

 sun fall upon the ice; they are very small 

 at first, but collect under the ice and form 

 larger bubbles. They consist of pure oxy- 

 gen gas. Neither during the night, nor dur- 

 ing the day when the sun does not shine, 

 are they observed to diminish in quantity. 

 The source of this oxygen is the carbonic 

 acid dissolved in the water, which is ab- 

 sorbed by the plants, but is again supplied 

 to the water, by the decay of vegetable sub- 

 stances contained in the soil. If these plants 

 absorb oxygen during the night, it can be in 

 no greater quantity than that which the sur- 

 rounding water holds in solution, for the 

 gas, which has been exhaled, is not again 

 absorbed. The action of water plants can- 

 not be supposed to form an exception to a 

 great law of nature, and the less so, as the 

 different action of aerial plants upon the at- 

 mosphere is very easily explained. 



The opinion is not new that the carbonic 

 acid of the air serves for the nutriment of 

 plants, and that its carbon is assimilated by 

 them ; it has been admitted, defended, and 

 argued for, by the soundest and most intelli- 

 gent natural philosophers, namely, by Priest- 

 ley, Sennebier, De Saussure, and even by 

 Ingenhouss himself. There scarcely exists 

 a theory in natural science, in favour of 

 which there are mo \lear and decisive ar- 



guments. How, then, are we to account 

 for its not being received in its full extent by 

 most other physiologists, for its being even 

 disputed by many, and considered by a few 

 as quite refuted ! 



All this is due to two causes, which we 

 shall now consider. 



One is, that in botany the talent and la- 

 bour of inquirers has been wholly spent in 

 the examination of form and structure : che- 

 mistry and physics have not been allowed 

 to sit in council upon the explanation of the 

 most simple processes ; their experience and 

 their laws have not been employed, though 

 the most powerful means of help in the ac- 

 quirement of true knowledge. They have 

 not been used, because their study has been 

 neglected. 



All discoveries in physics and in chemis- 

 try, all explanations of chemists, must re- 

 main without fruit and useless, because, 

 even to the great leaders in physiology, car- 

 bonic acid, ammonia, acids, and bases, are 

 sounds without meaning, words without 

 sense, terms of an unknown language, which 

 awaken no thoughts and no associations. 

 They treat these sciences like the vulgar, 

 who despise a foreign literature in exact 

 propoUion to their ignorance of it; since 

 even when they have had some acquintance 

 with them, they have not understood their 

 spirit and application. 



Physiologists reject the aid of chemistry 

 in their inquiry into the secrets of vitality, 

 although it alone could guide them in the 

 true path ; they reject chemistry, because in 

 its pursuit of knowledge it destroys the sub- 

 jects of its investigation ; but they forget 

 that the knife of the anatomist must dis- 

 member the body, and destroy its organs, if 

 an account is to be given of their form, 

 structure, and functions. 



When pure potato starch is dissolved in 

 nitric acid, a ring of the finest wax remains. 

 What can be opposed to the conclusion of 

 the chemist, that each grain of starch con- 

 sists of concentric layers of wax and amylin, 

 which thus mutually protect each other 

 against the action of water and ether'? Can 

 results of this kind, which illustrate so com- 

 pletely both the nature and properties of 

 bodies, be attained by the microscope 1 la 

 it possible to make the gluten in a piece of 

 bread visible in all its connections and rami- 

 fications ? It is impossible by means of in- 

 struments ; but if the piece of bread is placed 

 in a lukewarm decoction of malt, the starch , 

 and the substance called dextrine,* are seen 

 to dissolve like sugar in water, and, at last, 

 nothing remains except the gluten, in the 



* According to Raspail, starch consists of vesi- 

 cles inclosing within them a fluid resembling gum. 

 Starch may be put in cold water without being 

 dissolved : but, when placed in hot water, these 

 spherules burst, and allow the escape of the liquid. 

 This liquid is the dextrine of Biot, so called be- 

 cause it possesses the property of turning the 

 plane of the polarization of light to the right hand. 

 ED. 



