90 ANATOMY AND PHYSIOLOGY OF 



cess was elucidated in the simplest way. This theory conse- 

 qiiently met with "universal acceptation, and in all books the 

 decomposition of carbonic acid, taking place in the leaves, is 

 spoken of as a settled fact, but we are without one proof that 

 such is actually the state of the case. Liebig remarked, that it 

 was far more probable that it was not the difficultly deconiposable 

 carbonic acid, but the readily decomposable water which was 

 separated into its elements, and its oxygen given off, while its 

 hydrogen entered into combination with the carbonic acid. 

 The result was of course the same. There is no means of testmg 

 the correctness of either of these theories. But it is possible that 

 they are equally false, that the carbonic acid does not enter into 

 combination with the hydrogen of the water, but with another 

 substance contained in the plant, and that oxygen becomes free 

 by the decomposition of an organic substance previously formed. 

 The latter is the opinion of Mulder, who assumes that the plant 

 does not decompose carbonic acid because it is green, but while it 

 is becoming green; new chlorophyll is constantly forming under 

 the injluence of light, with this originate the wax and starch 

 associated with it, and an excretion of oxygen is necessarily con- 

 nected with this ; and this oxygen goes off partly in the form of 

 gas, and in part oxidizes the colourless chlorophyll, and converts 

 it into green. On the other hand, Draper, on account of the ex- 

 halation of nitrogen which he regards as necessary, assumes that 

 chlorophyll acts the part of a ferment in the process of decompo- 

 sition of carbonic acid, and in this itself suffers a decomposition, 

 in consequence of which nitrogen is set free. Thus, at the very 

 first step of the nutrition of vegetables, which was supposed to be 

 the most thoroughly investigated, opinions become divergent; 

 each has a certain probability, not one is proved. The only cer- 

 tainty is, that carbon and water remain within the plant, and are 

 applied to the formatiou of its organized, substance. ^ 



On the question of the combinations into which the absorbed 

 nutriment first enters, the views of chemists stand in no better 

 agreement. Saussure's experiments shewed that plants to which 

 cai^bonic acid and water were afforded, acquired increase of 

 weight equal to about twice the weight of carbon taken up. 

 It may be considered probable, as Davy assumed, that the car- 

 bon absorbed enters at once into a neutral combination with the 

 elements of water; in all probability this compound is soluble in 

 water; since, therefore, dextrine is found in all green coloured 

 organ>s, it is not unlikely that this, or in other cases, sugar is the 

 form under which the said inorganic substances combine into 

 organic substance. 



But another probability is opposed to this notion, that the con- 

 stituents of water and carbon enter at once into a neutral com- 

 bination. All plants contain, besides the neutral substances, 

 organic acids, in which the oxygen bears a greater proportion to 



