Chap, ii Photosynthesis 295 



a moderately concentrated solution of the pigment with 

 nascent hydrogen he found it transformed into a very pale 

 yellow liquid, which in the presence of traces of air or oxy- 

 gen resumes very rapidly its green appearance. This yellow 

 colouring matter, when in dilute solutions, is characterized 

 by a total absence of bands in the less refrangible part of 

 the spectrum ; in greater concentration it gives bands 

 nearly corresponding to bands 2 and 4 of the chlorophyll 

 spectrum, but no trace of band No. 1. He was able to 

 detect the presence of this pigment in etiolated seedlings 

 if he prepared the extracts in the total absence of light. 

 He could not satisfy himself of the presence of this reduced 

 constituent of chlorophyll in an ordinary green leaf, but 

 he pointed out that such demonstration must be extremely 

 difficult, if not impossible, on account of the readiness with 

 which it would be converted into chlorophyll on being 

 exposed to light. 



Timiriazeff gave the name protophyllin to this new pig- 

 ment. He was led by his discovery to the view that we 

 have to admit the existence of at least two states of oxida- 

 tion of the chlorophyll, which are readily transformed from 

 one to the other by the simple processes of oxidation and 

 reduction. He made use of this observation, as will be 

 pointed out later, in formulating a theory of the mode of 

 action of chlorophyll. 



A theory of the derivation of chlorophyll from etiolin 

 was put forward by Gris in 1857 and supported twenty 

 years later by Mikosch. It appears to have little to sup- 

 port it except the fact, observed by Pringsheim, Wiesner, 

 and others, that the two pigments are both contained in 

 the green parts of plants and perhaps in the same plastids. 

 The spectra of the two pigments have a general resemblance. 



The result of the investigations of the period into the 

 nature and chemical relationships of chlorophyll did not 

 then lead to very concordant results. All that appeared 



