STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 5 



a general theory which has met widespread success in its practical 

 bearing on agriculture. Their investigations deal in the main with 

 the relation between vegetation and fruit setting and nitrate fer- 

 tiHzation. They have been able to differentiate the carbohydrate- 

 nitrogen relations of certain plants on the basis of their vegetative 

 and sexual activities. 



There exists very httle exact information regarding the general 

 course of formation, synthesis, or fate in the general metabolism 

 of any of the organic nitrogen compounds in higher plants. The 

 number and variety of different types of nitrogenous substances 

 found in plants are enormous, and it appears an almost hopeless 

 task to unravel the tangle of chemical reactions which lead to this 

 multiplicit}^ of compounds. It seems, however, quite erroneous to 

 class together the various types of nitrogen compounds, such as the 

 proteins and related substances, the amino-acids, amides, etc., and 

 regard their phj'^siological functions as being the same or even very 

 intimately connected. An insight into this complex of chemical 

 reactions comprising metabolic energesis can, of course, be obtained 

 only through laborious experimental investigation involving much 

 observational and chemical-analytical work with living plants. 

 Chemistry can offer no short cuts, but rather supplies the instruments 

 with which to illuminate these hidden activities. Nor can the 

 conceptions of chemistry always find immediate application to reac- 

 tions in living organisms. Thus the many theoretical speculations 

 regarding the chemistry of the photosynthetic process have contrib- 

 uted very little to the solution of that problem. This is true also 

 of the chemical speculations regarding the formation of the amino 

 acids and the proteins, although there are a number of elaborate 

 theories which have been formulated to explain this complex process.^ 

 To these the warning of Pfeffer applies very aptly, which is to the 

 effect that it is a very confusing error to presume that an organism 

 must, in its metabolic economy, follow a course which seems to man, 

 under the influence of existing chemical and physical knowledge, 

 the most plausible course. All of these theories are still dealing with 

 probabilities supported by very little experimental physiological 

 evidence. Moreover, plant chemistry can hardly claim to be an 

 independent science. The great advances which have been made in 

 protein chemistry have been stimulated largely by animal physiology, 

 and progress in our understanding of plant proteins has been made, 

 in the main, by following the methods previously worked out for 

 proteins of animal origin. These studies seem to indicate that the 



1 LoEB, W. Ber. d. deutsch. chem. Ges., 46, 684-697 (1913). 

 Franzen, H. Jour. Prakt. Chem., 86, 133 (1913). 



Batjdish, O. Jour. Biol. Chem., 48, 489-502 (1921). Ber. d. deutsdi. chem. Gps., 46, 115-125 

 (1913); 49, 1159-1167 (1916); 50, 652-660 (1917); 51, 793-805 (1918); 52, B 35-43 (1919). 

 LoEW, O. Ibid., SO, 909-910 (1917). 



