138 THE KOLE OF NITRCXJEN IN PLANT-METABOLISM, v., 



to state that nitrification takes place in the plant-cells, and 

 especially in the stems — at least in those plants that are rich 

 in nitrate ; and that this process is similar to that of nitrifi- 

 cation in the soil, and is due to the same general function of 

 cells which gives rise to the oxidised acids, oxalic, malic, 

 and tartaric* These views were also held by Kreuslerf, 

 BelzungI, and others; and to understand them, it is neces- 

 sary to recollect that their experiments belong to the period 

 immediately preceding Winogradsky's classic work. 



However, their results have not been conclusively con- 

 firmed since, and they are entirely opposed to those of 

 Molisch and Frank§ and Schulze^, who hold that all the 

 nitrate in plants has been absorbed entirely through the 

 roots. 



For the higher plants, potassium nitrate has been shown 

 to be the more suitable nitrogen source, although some grow 

 just as well with ammonium salts. Pitsch**, however, has 

 shown that the presence of nitrate in the plant enables it to 

 take up more nitrogen in other forms, such as ammonia : and 

 in every case, except wheat, nitrate-plants utilised much more 

 of the other forms of nitrogen than the ammonia-plants did. 

 Ammonia does not accumulate in the plant, but, when de- 

 prived of light, acid-amides are formed, from which the 

 ammonia is readily recovered when required. On the other 

 hand, nitrates can be stored in the tissues as reserve-material. 



Demoussytt has shown that the living protoplasm possesses 

 the power of firm retention of nitrates ; so that, although 

 exceedingly soluble outside, the nitrates cannot be extracted 

 from the plant-cells by cold water. When, however, the 



* Berthklot et Andre. — Loc. cit., pp. 126, 128. 

 t Laiidw. .Tail lb., 1886, 309. 

 JJonrn. de Bot., 1893, 87. 



§ Ber. hot. Ges., 5, 1887, 472. 

 ^ Zeit. physiol. Chem. 22, 1896, 82. 

 ••'* Laudw. Versuchs-Stat., 42, 1892. 

 ++ C.R. 118, 1894, 79; 127, 1898, 771. 



