106 CAROTINOIDS AND RELATED PIGMENTS 



yellow and the other a violet colored substance. The latter was 

 regarded as Zopf s red carotinin. Its xanthophyll nature was shown 

 by its ready solubility in the phenol-glycerin reagent. The possibility 

 of this pigment being a potassium compound as it should be from 

 Zopf's description, inasmuch as it was produced in a strongly alka- 

 line medium (Molisch's reagent), was tested by treating the crystals 

 with dilute acid for 24 hours. No change was produced in their 

 properties. 



The red pigment of the blood algae deserves further study in the 

 light of the apparently conflicting observations of Zopf and van 

 Wisselingh. Its red color and xanthophyll-like properties as de- 

 scribed by the latter investigator suggests the red rhodoxanthin de- 

 scribed in Chapter II. No other carotinoids have yet been described, 

 however, which show acid properties and combine with alkalies as t la- 

 red algae pigment is stated to do. 



An interesting observation made by van Wisselingh in connection 

 with his study of the blood algae was that the plants had mostly green 

 aplanospores when cultivated in media containing 0.01 per cent each 

 of KN0 3 , (NH 4 ),HPO 4 , MgCl 2 , Na 2 S0 4 , but that the aplanospores 

 were mostly red when allowed to develop in media containing 0.02 per 

 cent NH 4 N0 3 , K 2 HP0 4 and MgS0 4 . Jacobsen (1913) has also studied 

 the conditions governing the formation of pigment in Haematococcus 

 pluvialis and found that temperature as well as food conditions influ- 

 ence it. He was unable to extract the pigment from the plant with 

 fatty oils, and it did not respond to Tswett's resorcin method for the 

 microcrystallization of carotinoid. 



The Bacillariea (Diatomaceae) . The diatoms are unicellular 

 algae of very peculiar structure and interesting habits. The single 

 cells are composed of two symmetrical valves which are held together 

 by a membranous sac of slightly colored protoplasm. The single 

 cells are lOu. or less in diameter. The valves of which they are con- 

 structed are frequently beautifully sculptured, and when many of the 

 cells unite, as is sometimes the case, very peculiar shaped structures 

 often result. The epidermis of the diatoms is composed of silica which 

 these organisms have the power to extract from the water in which 

 they develop. Deposits of silica from great growths of these plants 

 have considerable commercial value as diatomaceous earth. The 

 algae inhabit stagnant water, wet rocks and the sea. 



The diatoms comprise a considerable portion of the plankton of the 

 sea. It is this fact, together with the part which the plankton of the 



