PIGMENTS 115 



form (see Chapter XV), and, hence, cannot diffuse out through 

 the cell-walls. The only way in which they can be extracted 

 from the tissues is by rupturing the cells, by grinding with sharp 

 sand, etc., after which the pigments can readily be dissolved out 

 by water. 



Phycoerythrin is the red pigment. It is a colloidal, nitrog- 

 enous substance, allied to the proteins (see Chapter XIII) but 

 not a true protein compound. Hydrolysis by acids indicates 

 that it contains leucin and tyrosin, two amino-acids which are 

 constituents of proteins, along with other bodies of unknown com- 

 position. 



The colloidal solution of phycoerythrin in .water has a bril- 

 liant rose-red color, with an orange fluorescence. It readily sets 

 to a gel (see Chapter XV), so that the solution is almost impossible 

 to filter. On this account, purified solutions of this pigment are 

 very difficult to secure, and no satisfactory analysis to indicate its 

 composition has yet been obtained. 



Actinically, it is a complementary pigment to chlorophyll, 

 that is, it absorbs the blue and green rays and permits the passage 

 of light which is of the wave length that is absorbed by chlorophyll. 



Phycophaein. Still less is known of the composition of this 

 pigment than of that of phycoerythrin. It is the characteristic 

 pigment of brown seaweeds. It is supposed to exist in the cells 

 of algae, chiefly as a colorless chromogen, which becomes first 

 yellow and then brown on exposure to air. Associated with it are 

 other pigments, which have been variously reported as carotin, 

 phycoxanthin, etc. 



THE ANTHOCYANS 



These are a group of pigments of red, blue, or violet color, 

 which occur in the flowers, fruits, or leaves of many species of 

 plants. They are essentially ornamental pigments, and consti- 

 tute a large proportion of the brilliant colors of flowers, etc. 

 They occur not only dissolved in the cell-sap, but also as deposits 

 of definite crystals or amorphous compounds in the cell proto- 

 plasm. 



They are all glucosides. When the anthocyans are hydrolyzed, 

 the sugar molecules are split off and the characteristic hydroxy- 

 derivatives of the three-ring anthocyan nucleus (figured on page 



