530 Allgemeines. 



open to doubt whether they correspond to Chlorophyll at all 

 and not rather to some products of its decomposition. 



By projecting a spectrum of sufficient intensity onto a green 

 leaf and applying the iodine-starch test a well-defined absorption 

 spectrum of Chlorophyll with its principal band between B and 

 C and a gradual falling off towards the blue end is imprinted 

 on the leaf. 



The blue and violet rays produce hardly any effect at all. 

 This last result may be principally attributed to the fact that 

 the appearance of starch is only the resultant of two conflicting 

 processes — its production and dissolution — so that, at a 

 certain point, when the assimilation is not sufficiently intense, 

 the former may be counterbalanced by the latter. 



Turning to the more refracted half of the spectrum an 

 experiment was conducted in the following manner: a beam of 

 light, reflected by a large Foucault Heliostat and Condensed on 

 the slit by a lens was decomposed by a directvision prism and 

 recomposed into two bunds of yellovv and blue light. The 

 results may be stated thus : If the quantity of carbon dioxide 

 reduced by the yellow half be represented by 100 the effect of 

 the blue half will be 54, and the conclusion is that the effect 

 of the blue and violet rays has hitherto been somewhat under- 

 rated. The same result has been obtained with the iodine- 

 starch test. The fact that the reduction of carbon dioxide and 

 the production of starch are due to rays absorbed by the 

 Chlorophyll may be considered as fully proved, the more so as 

 a bolometric study of the Chlorophyll spectrum in the infra-red 

 by Donath has shown the absence of absorption bands in 

 this region. This accounts for the fact that no reduction can 

 be attributed to the rays filtered through Tyndall's iodine 

 Solution. 



Timiriazeff points out a flaw in the applicabitity of 

 Herschel's Law to the photosynthetic process. It applies to 

 the decomposition of Chlorophyll, but in the reduction of carbon 

 dioxide we are dealing with the decomposition of a colourless 

 gas, the light being absorbed by another substance, Chlorophyll. 



Vogel's discovery of optica! sensitisers supplied the link 

 required. If a sensitive plate be exposed to a spectrum of 

 Chlorophyll the effect stops short at the line D. But if the 

 plate be previously treated with a Solution of sodium chloro- 

 phyllate there is a bright band produced corresponding to the 

 principal absorption band between B and C. Chlorophyll is, 

 according to the author, rapidly decomposed by light, and it is 

 shown that the rays effective in this are just those which effect 

 the reduction of carbon dioxide. Timiriazeff also finds that 

 Chlorophyll is a chemical sensitiser absorbing a product of the 

 chemical action, namely oxygen, and thus continually disturbing 

 the equilibrium between the carbon dioxide and the products 

 of its decomposition. There would appear to be two forms of 



