THE METABOLISM OF PLANTS. 149 



materials, we can only guess at the probable process. Em- 

 merling, from a series of analyses of the Bean ( Vicia Faba var. 

 major], comes to the conclusion that the nitrates absorbed by 

 the root are decomposed by the organic acids (especially the 

 oxalic) present in the plant with liberation of nitric acid, and 

 that this nitric acid is then used in the formation of proteid. 

 According to Holzner it is probable that the absorbed sul- 

 phates also are decomposed by the organic acids, sulphuric 

 acid being set free. It is doubtless by the combination of 

 the nitric and sulphuric acids formed under these conditions 

 with some form of non-nitrogenous organic substance, Loew 

 and Bokorny suggest formic aldehyde, that nitrogenous 

 organic substance is ultimately produced. 



In the detailed discussion of this difficult subject we will 

 principally direct our attention to the highly organised plants, 

 for our knowledge of their chemistry is relatively great. We 

 will begin by ascertaining what organ it is in which the 

 formation of nitrogenous organic substance takes place. 



From what has just been said respecting the origin of the 

 starch which is to be found in the chlorophyll-corpuscles, 

 there can be no doubt that proteid is formed in cells which 

 contain this substance ; and since it is so abundant in leaves, 

 we may conclude that the leaf is more especially the organ in 

 which the formation of proteid takes place. Moreover this 

 conclusion is supported by other though less direct evidence. 

 Emmerling observed in the Bean that whereas the root con- 

 tained a quantity of nitric acid (0.0756 per cent.) and the stem 

 also (0-0891 per cent in the lower part, 0-0238 per cent, in the 

 upper), no trace of it could be detected in the leaves ; from 

 this he inferred that it is in the leaves that the nitrates 

 absorbed by the roots and conveyed through the stem are 

 used up in the formation of nitrogenous organic substance. 

 Further, Pott found that the proportion of proteid in the plant 

 increases from the roots towards the leaves, the proportion of 

 proteid in the leaves being about twice as great as that in the 

 roots of many of the plants which he analysed. 



With regard to the chemistry of the process, there can be 

 little doubt that proteid is not directly formed, but that nitro- 



