lo Carbon Assimilation. 



and violet. The spectrum of the brown algal thallus on the other 

 hand is not at all like this, but is not much different from that of 

 the green leaf. On putting into boiling water a change in the 

 spectrum is observed similar to that observed in the case of the 

 green leaf and this can be explained in a similar way by supposing 

 a change in the chlorophyll from the colloidal condition to a solution 

 in fats and waxes. 



A microscopic examination of the thallus before and after 

 treatment with hot water confirmed other lines of evidence. 



As regards the composition of the pigments in the brown alg89 

 some workers, including Tswett, have supposed a third chlorophyll 

 to be present ; Tswett, for example, speaks of chlorophyll y. 

 Willstatter, however, could find no sign of such a substance when 

 he treated fresh brown algae with cold solvents. But he has 

 obtained this third chlorophyll derivative from stale or dried thallus. 

 It is clear that the chlorophyll of the brown algas changes on 

 standing, and the pigment is unstable in the dried plant. 



The result of Willstatter's researches on the pigments of the 

 brown algae is to show that the same pigments are present in their 

 plastids as in the chloroplasts of the green leaf, and that a third 

 yellow pigment, fucoxanthin is present in addition, a pigment with 

 the formula C4oH5gOe. The green pigment is nearly all 

 chlorophyll a ; only traces of chlorophyll b were found. Willstatter 

 gives the result of analyses of Fucus, Dictyota and Laminaria. The 

 yellow pigments are much more abundant than in green plants. 

 Instead of being present in the molecular ratio of 3 to 5 of green to 

 1 part of yellow pigment as in higher plants, the ratio is here more 

 nearly 1 to 1. 



Willstattergives the following figures as the result of his analysis 

 of Fucus pigments : — 



Chlorophyll 0-503 



(nearly all a, not more than 5% b). 



Carotin ' o-089 



Xanthophyll ... ... ... ^ 0-087 



Fucoxanthin ... ... ... ^^. 0-169 



These numbers represent parts per 1,000 of the fresh thallus 

 The molecular ratios are : — 



Chlorophyll ... .,. ... 3.g^ 



Carotin j.Qg 



Xanthophyll j.qq 



Fucoxanthin ... ... ... j.yg 



