i6o Carbon Assimilation. 



a photochemical reaction ; in Siegfried's view on the other hand 

 the first stage of carbon assimilation is a purely chemical process, 

 and the photochemical reaction occurs in a complex carbon com- 

 pound. This suggestion of Siegfried's has been as completely 

 neglected by plant physiologists as that of van't Hoff, although it 

 offers possibilities of connecting carbon assimilation with nitrogen 

 assimilation in a way which is not possible on the Baeyer 

 hypothesis. 



Further interest in Siegfried's suggestion should result from 

 the extensive researches ofCiamician and Silber (1901-1915) on the 

 photochemical reactions in complex organic compounds. Willstatter 

 and Stoll (1915b-d) seem unaware of the work of Siegfried, but 

 express almost identically the same view in regard to the accumula- 

 tion of carbon dioxide in the protoplasm by means of proteins. 



E. Theories of Willstatter. 



It cannot be said that the development of plant physiology 

 during the last hundred years has been very rapid, nor is the 

 position which it occupies among other branches of botanical 

 science worthy of its importance. This is no doubt largely due to 

 lack of knowledge of the fundamental sciences, physics and 

 chemistry, which must form the basis of all science which is not 

 merely cataloguing or descriptive. As a consequence of this when- 

 ever chemists have put forward contributions to the theory of 

 plant processes, their statements have usually been accepted by 

 botanists without reserve. That this has been much to the detriment 

 of plant physiology is evident from a survey of the history of the 

 subject. It is only to be expected that theories of pure chemists on 

 plant physiological subjects should be misleading, when one con- 

 siders how infinitely more complex are the conditions in the plant 

 compared with the moderately simple laboratory conditions of 

 ordinary chemical experiments. This was true sixty or seventy 

 years ago, and it is true to-day. 



Willstatter, whose brilliant chemical work has been, and pro- 

 bably will be in the future, of so much value to plant physiology, 

 has, like the eminent chemists Liebig and Baeyer before him, 

 ventured to put forward theoretical views on the processes of 

 carbon assimilation. Below we give a translation of the first 

 instalment of his theory published in 1906 (p. 64) under the sub- 

 heading of " The Life of the Plant." 



" Plants and animals live by means of the catalytic action of 



