158 LIGHT, VEGETATION AND CHLOROPHYLL 



This theory was, in many respects, attractive and had many 

 supporters. But is it true that chlorophyll combines with 

 carbon dioxide? 



On closer consideration, the weakness of these theories 

 becomes apparent. They claim to solve the problem as simply 

 as possible, but this simpUcity, striking enough when the 

 formulae are set out on paper, ignores life and the nature of 

 Uving things. It has, in fact, not been possible to discover in 

 the hving organism any of the intermediate substances through 

 which carbon passes as it is being transformed into glucosides 

 and which, in the theories, are assumed to be necessary. 



New Techniques 



In the last twenty years the situation has changed. Through 

 the study of the phenomena of fermentation and of respiration, 

 we have begun to understand the working of the Uving 

 organism; instead of effecting violent reactions, it degrades 

 energy progressively through all the intermediate stages of 

 oxidation-reduction. 



The use of radioactive isotopes has revealed some of the 

 intermediate reactions. This technique is described in Chapter 

 VIII of Part I {Light and Vegetation). 



The technique of chromatography has also been used to 

 separate the chemical substances in solution. As it spreads 

 out on a filter-paper, a solvent carries the different substances 

 dissolved in it to a certain distance. Under the same con- 

 ditions, a given substance is carried to a given distance and is 

 separated in this way from the others by the use of an appro- 

 priate solvent. To effect a better separation, two solvents are 

 used successively on the same paper and are made to spread 

 out at right angles, e.g., one from the bottom and the other 

 from the right-hand side. If the two solvents were identical 

 and the starting point placed at the bottom on the right, the 

 substances would be distributed on a diagonal from their 

 starting point; but as the solvents are different and do not 

 carry the dissolved substances to the same distance, the latter 

 are distributed over the whole surface at different and precise 



