CAROTINOIDS !.\ Till'. CRYPTOGAMS 107 



sea plays in the food of marine animals which makes the pigments 

 of the diatoms of inteiv-t. Most species of diatoms have a brownish 

 color. A few are green and probably contain chlorophyll, or at least 

 one of the chlorophyll pigments. Of the many thousands of species 

 which are known, unfortunately only a few have been examined for 

 carotinoids. However, these are probably to be considered as typical 

 of the remainder. 



The earliest workers regarded the color of the diatoms as due to a 

 single pigment to which Niigeli (1849) gave the name diatomin. This 

 name was adopted by Askenasy (1867) for the brownish yellow pig- 

 ment which could be extracted with alcohol, and which he described 

 as showing a strong absorption of the blue half of the spectrum and 

 a characteristic intense blue-green color on addition of H 2 SO 4 or HC1 

 to the alcoholic solution. Nebelung (1878) extracted a yellow pig- 

 ment from M^< losira species with petroleum ether but called it phyco- 

 xanthin. The principal pigment extracted in this case may have been 

 carotin. 



Further proof of the carotinoid nature of the Bacillariea pigments 

 was furnished by Tammes (1900), who obtained the Molisch test on 

 Fragilaria species and by Kohl (1902) who obtained the same test on 

 Gomphonema and Navicula species. Molisch (1905), himself apply- 

 ing the test to Nitzschia Palea, Nitzschia sigmoidea, C ymatopleura 

 solea and Pinnultiria viridis (Navicula viridis), obtained only yellow 

 drops, but these gave the chromolipoid color reactions with H 2 S0 4 

 and iodine. 



The conclusions of the various investigators are somewhat conflict- 

 ing regarding the exact nature of the carotinoids present in the silice- 

 ous algff. Zopf (1900) concluded that "cuearotin" (true carotin) 

 is the chief pigment present in Gomphonema, but that the pigment 

 differs somewhat from the carotin of other plants. Kohl (1906a) 

 concluded that the liver-colored diatoms, Achnanthidiwn lanceolatum 

 and Eunotia (Himanthidium) pectinalis, owe their color chiefly to 

 carotin with a little of his so-called (3-xanthophyll (which is not 

 carotinoid in the true sense) present also, as well as traces of chloro- 

 phyll. Kohl had previously (1902) concluded that the pigment known 

 as diatomin is carotin. Especially interesting is the observation of 

 Molisch that the species which he examined (1905) gave the so-called 

 leucocyan react inn winch is apparently specific for fncoxaiithin. 

 Askenasy (1867) had observed the same reaction for alcoholic ex- 

 tracts of diatoms, so that there are at least strong indications that 



