84 Ingvar Jorgensen and Walter Stiles. 
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 of Ciamician 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 
