PHYCOPHAEIN 261 



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 t 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 

 glucosides or may be decomposition products of proteins. 

 These pro-chromogens, by the action of enzymes, give origin 

 to chromogens. 



Chromogens are widely distributed in the vegetable king- 

 dom, in fact are universally present in those parts of plants 

 which are respiring ; they, however, vary in amount at differ- 

 ent seasons of the year and according to the physiological 

 condition of the plant. For instance, in the spring they occur 

 in abundance in the young leaves, and in the autumn the old 

 and dead leaves also contain much owing to the lack of co- 

 ordination of enzymic activity. 



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



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



J. See Blackman: " New Phytologist," 1904, 3, 237. 



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



