1 68 Carbon Ass imitation. 



Blackmail has brought out the important relation between 

 environmental factors and carbon assimilation, and has formulated 

 the principle of limiting factors in regard to their co-operation. 

 However, absolute rules cannot be made as to amount of assimilation 

 under any definite environment, owing to the complexity introduced 

 by the existence of unknown internal factors. Willstatter has 

 attempted to analyse the internal factors, and has brought proof 

 that chlorophyll is not the only internal factor, though what other 

 internal factors there are Willstatter's work does not show. Future 

 work will have to investigate the inter-relation between the internal 

 factors as well as the co-operation between the internal and external 

 factors. 



However, the internal factors operative at any moment are a 

 product of hereditary factors and environmental factors. It seems 

 likely that an application of the principles of genetics may prove 

 helpful in the analysis of internal factors in assimilation, and this 

 application may give a method for controlling some internal factors. 

 The aim, at present, of investigations on carbon assimilation is 

 to be able to tell the assimilatory power of a plant with a known his- 

 tory as regards environmental and hereditary factors when it is placed 

 in a known environment. Then it becomes of industrial importance to 

 discover how environmental factors can be modified so as to give the 

 maximum assimilation in relation to the inherited internal factors. 

 We should like to emphasize that the popular idea that under 

 natural conditions any particular factor, as for instance, light, is 

 nearly always in excess, while some other factor, as for instance 

 carbon dioxide, is nearly always limiting, is not justified. The power 

 of the plant to utilise any environmental factor must undergo 

 diurnal and seasonal variations depending on the interplay of the 

 other factors. 



For instance the environmental factors, radiation and temper- 

 ature, undergo daily and seasonal variations while although in regard 

 to the carbon dioxide supply not much information is to be had, 

 undoubtedly considerable variations occur (see, for example, Krantz, 

 1909). In this connection may be mentioned the work of Kraus 

 (1911) who successfully shows how great may be the variations in 

 environment over a very small area. 



The importance of work on carbon assimilation depends not 

 merely on its value in plant physiology and on its application in 

 agriculture, but also, as we have emphasized in our introductory 

 chapter, for the utilisation of radiant energy. For this reason in 



