1903.] The Oosmical Function of the Green Plant. 441 



refrangible part of the spectrum, but when sufficiently concentrated, 

 it shows a very distinct band nearly corresponding to the II band 

 of chlorophyll and another band about the place of the IV, no traces 

 of the principal band I being present. It was the first case of a 

 product of chlorophyll characterised by the total absence of what had 

 been considered the principal characteristic of the chlorophyll spectrum. 

 It is evident that we have here a reduced constituent of chlorophyll, 

 from which chlorophyll is regenerated almost instantaneously on its 

 being brought into contact with the oxygen of the air. 



Having obtained these important reactions of reduction and re- 

 generation of chlorophyll in its solutions, I took all possible pains to 

 find out the existence of this protophyllin in the living plant. The 

 formation of chlorophyll in etiolated seedlings being a process of 

 oxidation (the fact was demonstrated in my laboratory by Dementieff 

 in 1873), it was quite natural to search in etiolated seedlings for this 

 protophyllin so easily convertible into chlorophyll on being oxidised. 

 The facts exposed in the current literature were rather discouraging, 

 the so called Etiolin of the German botanists always presenting the 

 characteristic chlorophyll spectrum. My first steps were also unsuccess- 

 ful. I obtained, it is true, solutions where the second band was rather 

 more pronounced ; in some cases it had even the same intensity as the 

 first band, but I looked in vain for solutions in which the first band 

 would be totally absent, until the idea struck me that the precautions 

 generally taken were not sufficient to eliminate completely the influence 

 of light. I inclosed the small pots with the seeds that were intended to 

 germinate (sunflower seeds proved to be best) in tin cases, which in 

 their turn were kept in a cupboard in a photographer's dark room. The 

 solutions were prepared in the same dark room, all the precautions 

 used in orthochromatic photography being taken. The result was that 

 I obtained solutions of protophyllin without the least traces of the 

 chlorophyll spectrum. 



The colouring power of these solutions being very small, they had to 

 be studied in tubes 50 cm. long. In general about ten or twenty 

 cotyledons were used for preparing the necessary solution for filling the 

 tube. But it was sufficient to expose a single cotyledon, or even a part 

 of one, for an instant to the light in order to obtain a solution that 

 would present the characteristic chlorophyll bands. These facts 

 suffice to prove that in the living plant there exists a colouring matter 

 with the properties of reduced chlorophyll, almost instantaneously con- 

 vertible into chlorophyll on being exposed to light. 



Of course it would be of still greater importance to obtain a direct 

 proof of the presence of this reduced constituent of chlorophyll in the 

 green leaf ; this fact alone could account for its playing the part of a 

 chemical sensitiser ; but the detection of this substance in the green 

 leaf must needs present certain difficulties. As I have just insisted, the 



