NITROGENOUS METABOLISM 465 



(Sect. 93) to cause the starch to be retained intact while the amides formed by 

 proteid-decomposition are continually removed 1 . 



The importance of asparagin as translocatory material is sufficiently evident, 

 and it is obviously erroneous to regard it as an excrete product of metabolism, 

 as Prianischnikow 2 has recently done, thus upholding the view originally put 

 forward by Boussingault. 



SECTION 81. Nitrogenous Metabolism (continued], 



The various synthetic processes already mentioned probably all involve 

 a more or less complicated series of operations, and indeed it is only by 

 such means that a fungus can possibly exist when fed solely with proteids. 

 Even when proteids are assimilated along with carbohydrates, the quanti- 

 tative and qualitative differences between the nitrogenous end-products 

 form a sufficient indication that the course of metabolism may follow widely 

 different paths in different plants and also in the same plant under varying 

 circumstances. 



When similar products are produced from different carbohydrates it is 

 impossible to say whether the processes become identical before this 

 particular metabolic activity is completed or only during the very last 

 stage, and similarly it is impossible to say whether a difference between 

 the nitrogenous end-products is due to a change occurring immediately 

 a proteid molecule is assimilated or only at a later stage in the ensuing 

 chain of reactions. Moreover, it is impossible to say whether any amides 

 that may appear have been formed directly by proteid-decomposition, or 

 have perhaps been formed synthetically from ammonia or other disintegra- 

 tion-products. Amides are actually formed synthetically during the growth 

 of many of the higher plants (Sect. 71), but the amides which appear during 

 the mobilization of reserve food-materials do not seem to be produced in this 

 manner. 



It may, however, safely be concluded that owing to the reactive power 

 and regulatory activity which every plant possesses, the mode of formation 

 of amides may vary in the same plant under different nutritive and cultural 

 conditions. Thus Schulze :! found that glutamin usually preponderated in 

 cucumber seedlings, but that occasionally asparagin was most abundant, 

 while green plants of Lnpiwes lutcus contained leucin in addition to the 

 usual asparagin, whereas in etiolated plants amido-valerianic acid and 



1 For a comparison between proteid and carbohydrate metabolism, see the values given by 

 Prianischnikow (Versuchsst., 1895, Bd. XLV, p. 262) for Vicia saliva. 



2 Prianischnikow, Versuchsst., 1896, Bd. XLVI, p. 458. 



3 E. Schulze, Zeitschr. f. physiol. Chemie, 1896, Bd. xxn, p. 411; 1894, Bd. xx, p. 308 ; 

 Versuchsst., 1896, Bd. XLVIII, p. 53. 



PFEFFER H h 



