PLANT PRODUCTS 579 



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, CH 3 .OH.OCH 3 .CHO. Vanillin occurs abundantly in solution in 

 the pods of vanilla, or in the dry pods it occurs in an amorphous condition. 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 diffi- 

 culty 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 certain aromatic compounds. 



Veratrine, CsrHsaNOn. 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 examined under a microscope, it is to be seen 

 that the walls or cell-contents containing veratrine assume a yellow color, which 

 soon changes to an orange-red, and finally to a dusky violet. 



Wax. Wax frequently occurs in plants as a crust-like, or granular, or rod-like 

 layer over the cuticle. It consists of fats and free fatty acids, together with other 

 substances. Wax is insoluble in water, but it will melt and form droplets in water 

 at iooC. It is hardly soluble in cold alcohol, but will quickly dissolve in boiling 

 alcohol. When sections containing wax are heated in a solution of alcannin in 

 50 per cent, alcohol, the wax runs together in droplets, which become stained red by 

 the alcannin. Wax is not wetted by water, and sections are best mounted for 

 study in cold alcohol, which will dissolve the wax but little, if at all. 



Wound Gum. The wounded surfaces of deciduous trees become protected by 

 the formation of wound gum from starch contained in the live cells. Sections 

 taken through the wounded surfaces of such plants several days after the wound has 

 been inflicted show brownish granules of wound gum in the medullary rays, tracheal 

 tubes, and wood-cells. The wound gum may be found lying free in the cytoplasm 

 or surrounding starch-grains which have contributed to the formation of the gum. 

 Wound gum is not soluble in warm water, but may be dissolved in hot nitric acid 

 or in eau de Javelle after several hours. It is not soluble in sulphuric acid, potas- 

 sium hydrate, alcohol, or ether, but it may be dissolved in alcohol after treatment 

 for a few minutes with a solution of potassium chlorate in dilute hydrochloric acid. 

 It may be stained with a solution of fuchsin, iodine green, safranin, or methyl- 

 green. It is stained red by phloroglucin and hydrochloric acid. 



Xanthin, CsHUN^j. Xanthin occurs in an amorphous condition or in the form 

 of granules in yellow chromoplasts. It differs from carotin in being more soluble 

 in alcohol, and in being deposited in amorphous and resin-like masses on the evap- 

 oration of its solvent. It is insoluble in water, and but little soluble in ether and 

 benzine. It becomes green and then blue when treated with sulphuric acid, and 

 with potassium iodide-iodine it is colored green. 



