366 MICROCHEMISTRY OF PLANT PRODUCTS 



of the benzol; whereas, when sections containing caffeine are 

 treated in like manner, the crystals containing caffeine take on 

 the form of needles. 



Tyrosin, CeH.OH.CH^.CHNH^.COOH.— Tyrosin may be 

 demonstrated in abundance in the tubers of the Dahlia. When 

 sections are mounted under a coverglass in glycerine for several 

 days, needle-shaped crystals of tyrosin are deposited in radi- 

 ating groups. In an abundance of glycerine the crystals are not 

 deposited, for the reason that the tyrosin becomes too much 

 diffused through the glycerine. The crystals appear brownish 

 by transmitted, and white by reflected, light. When a portion 

 of a Dahlia tuber is placed in a dish of about the same size 

 as itself, and covered for about two-thirds of its length with 

 alcohol, an abundance of tyrosin crystals will collect at the 

 exposed cut surface. The crystals of tyrosin are colored a deep 

 red by means of Millon's reagent, and when nitric acid is poured 

 over them and then evaporated, a yellow residue is left. 



Vanillin, CeH3.0H.,OCH3.CHO.— The aldehyde vanillin 

 occurs abundantly in the dry, but not in the fresh, pods of Vanilla. 

 It is often found in a crystalline condition on the surface of dried 

 pods. It is soluble in alcohol and ether, and to a certain extent 

 in hot water, but it is soluble with difficulty in cold water. 

 When sections containing vanillin are wetted with a 4 per cent, 

 solution of orcin, and then treated with concentrated sulphuric 

 acid, they take on a deep carmine-red color; and when they are 

 treated in like manner with a solution of phloroglucin in place of 

 the orcin, a brick-red color is produced. It seems probable that 

 vanillin is always present in lignified walls, judging from the 

 colors which these assume with phloroglucin and orcin. 



Veratrine, Cg^H^gNO^j. — The alkaloid veratrine occurs in 

 the tissues of Veratrum album. When sections are placed in a 

 mixture of i drop of concentrated sulphuric acid and 2 drops of 

 water on a glass slide, and exaniined under a microscope, it is 

 to be seen that the walls or cell-contents of the cells containing 

 veratrine assume a yellow color, which soon changes to an orange- 

 red, and finally to a dusky violet. 



