PHYCOPHAEIN 251 



does not give the biuret reaction. It is impossible to say any 

 thing more definite regarding its chemical nature until it has 

 been prepared in a pure state in quantities sufficient for analysis. 

 Physiologically, phycoerythrin acts as a pigment com- 

 plementary to chlorophyll. It absorbs the blue-green rays, 

 and degrades them to yellow and red light of just those wave- 

 lengths which the chlorophyll can absorb. 



PHYCOPHAEIN, 



As is well known, a brown colouring matter may be 

 extracted by water from the Phaeophyceae and other brown 

 Algae. Hitherto this has generally been considered to be 

 due to the presence within the cells of a definite colouring 

 matter of a protein nature. According, however, to the work 

 of Molisch * and Tswett,f this is not the case. The brown 

 colouring matter is really due to post-mortem changes, the 

 oxidation of a water soluble chromogen. An extract pre- 

 pared with distilled water is at first colourless, but will turn 

 yellow if the solution is made alkaline in reaction, e.g. by tap 

 water, and finally brown owing to oxidation. If the reaction 

 be made acid decolorization will result. With regard to the 

 chemistry of this substance little, if anything, is known. 



Tswett finds that the natural colour of brown sea-weeds is 

 due to the presence of several pigments in the chloroplast, 

 amongst which is carotin, but until more information regarding 

 the relationships between these and similar pigments is avail- 

 able, it is hardly profitable to consider them further. 



With regard to the physiological significance of these pig- 

 ments in the Algae, the work of Gaidukov I on complementary 

 chromatic adaptation may be consulted. 



Although it is not proposed to enter into a detailed con- 

 sideration of the phenomena of respiration here, brief men- 

 tion may be made of Palladin's § conceptions on the subject 

 on account of the role he ascribes to colouring matters and 

 allied substances in respiratory activity. 



Occurring in plants are pro-chromogens which may be 



* Molisch: " Bot. Ztg.," 1894, 52, 181 ; 1895, 53, 131; 1905, 63, 131- 



+ Tswett: " Ber. deut. bot. Gesells.," 1906, 24, 235. 



XSee Blackman : " New Phytologist," 1904, 3, 237. 



§ Palladin : " Ber. deut. bot. Gesells.," 1908,26a, 125, 378, 389 ; 1909,27, no. 



