342 MICROCHEMISTRY OF PLANT PRODUCTS 



ammonia produces a dark gray precipitate, picric acid a yellow, 

 and potassium iodide-iodine a deep reddish-brown precipitate. 



Crocin (Saffron-yellow), C^^H^gOjg- — This is a glucoside 

 occurring in the stigmas of Crocus sativus. When concentrated 

 sulphuric acid is added to crocin, a deep blue color is produced 

 which passes into violet, cherry-red and then brown. Nitric 

 acid also produces a blue color which passes into brown. 



Curarin. — This alkaloid occurs in the parenchyma and bast 

 of several species of Strychnos. Concentrated nitric acid pro- 

 duces with it a blood-red, and dilute or concentrated sulphuric 

 acid a carmine-red color. 



Curcumin, Cj^Hj^O^. — Curcumin occurs, dissolved in an 

 ethereal oil, in certain cells of the ground parenchyma of the 

 rhizome of species of Curcuma and probably in other members 

 of the Zingiberaceae family. It crystallizes in the form of yellow 

 needles which have a bluish tint by reflected light. Lead ace- 

 tate forms a brick-red precipitate with curcumin, and sulphuric 

 acid gives it a crimson color. 



Cutin. — Cutin is a substance which is nearly related to suberin 

 (which see), but is not identical with it. None of the acids 

 derived from cutin is identical with any derived from suberin. 

 However, the micro-chemical reactions of suberin and cutin are 

 the same. They are insoluble in concentrated sulphuric acid 

 and cuprammonia, and are colored from yellow to brown with 

 the iodine reagents. When heated with concentrated potassium 

 hydrate, they form yellowish droplets and granular masses. 

 When heated in nitric acid and potassium hydrate, they form 

 droplets which melt between 30° and 40° C, and which are solu- 

 ble in boiling alcohol, ether, benzol, chloroform and dilute potas- 

 sium hydrate. Both suberized and cutinized walls resist con- 

 centrated chromic acid at ordinary temperatures. Chemical 

 analysis shows that cutin is composed of compound esters and 

 fatty acids, and when heated to 300° in glycerine, it behaves as a 

 fatty body. For staining cutinized walls, see under Cyanin, 

 Alcannin, Chlorophyll Solutions. 



Cytisin, CuHj^NjO. — This alkaloid occurs in the seeds of 



