Carbon Assimilation. 
249 
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 algfe 
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 algae 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 C 40 H 6e O 6 . 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 jellow 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 ... ... ... ... 0‘089 
Xanthophyll ... ... ... ... 0‘087 
Fucoxanthin ... ... ... ... 0‘169 
These numbers represent parts per 1,000 of the fresh thallus. 
The molecular ratios are : : — 
Chlorophyll 
Carotin 
Xanthophyll 
Fucoxanthin ... 
... 3-64 
... 1-08 
... 100 
... 1-75 
In the following sections of this chapter we propose to deal 
more in detail with the chemistry of the pigments, their method 
