The Pigments of the Leaf. 9 



the same four pigments as are present in higher plants, but the alga 

 is comparatively richer in chlorophyll b and also contains, relatively 

 to the chlorophyll, more of the yellow pigments than is present in 

 the green leaves of land plants. Willstatter gives the following table 

 for the pigments of Ulva, the numbers representing parts per 

 thousand of fresh thallus : — 



Chlorophyll a... ... ... ... 0-16 



b... ... ... ... 0-12 



Carotin ... ... ... ... 0-02 



Xanthophyll ... ... ... ... 006 



The brown algse stand of course in great contrast to the green 

 algse and higher plants as far as theii' external appearance goes in 

 the matter of colour, and many views have been held in regard to 

 the presence of pigments causingthis colour. ThusCohn (1865, 1867) 

 supposed the cells of the Phaeophyceae contained a brown pigment 

 called phaeophyll nearly allied to chlorophyll. Molisch (1905) 

 supported this view. In these brown forms he supposed the only 

 pigment present to be a brown chlorophyll derivative which changes 

 easily intoordinary chlorophyll when the thallus is immersed in warm 

 air or water or is treated with organic solvents. Potassium hydroxide 

 reacts with chlorophyll to produce a brown derivative which easily 

 gives rise to green compounds, and with this brown derivative he 

 compares phaeophyll. 



The theory generally taught in this country, which is the one held 

 byTswett (1906, 1910) and Czapek( 1911), is that chlorophyll is present 

 in the plastids of the brown algas but that its presence is masked by 

 yellow pigments. The well-known class experiment of putting the 

 thallus of a brown alga in boiling virater which results in an immediate 

 change of brown to green, is usually explained by supposing the 

 brown covering pigment to be extracted by the water. Tswett 

 Suggests as an alternative explanation the alteration of the yellow 

 pigment. 



The completion of the proof that chlorophyll is actually present 

 in the brown algae has been made by Willstatter and Page (1914). 

 These workers in dealing with the phEeophyll theory of Cohn and 

 Molisch show that if the algse contained a pigment similar to that 

 produced by the action of potassium hydrate on chlorophyll it would 

 give different derivatives when subjected to different treatments, but 

 this is not the case. 



A second argument against IWolisch's view is to be found in 

 spectroscopic examination of the pigments. The brown chlorophyll 

 derivatives give a spectrum quite different from that of chlorophyll, 

 there is no absorption in the red, but strong absorption in the green 



