WAX XANTHINE 367 



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

 ular, 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 100 C. 

 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 in- 

 flicted 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 water after several hours. It is not 

 soluble in sulphuric acid, potassium hydrate, alcohol, or ether, 

 but it may be dissolved in alcohol after treatment for a few min- 

 utes 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. 



Xanthine, C 5 H 4 N 4 O 2 . Xanthine occurs in an amorphous 

 condition or in the form of granules in yellow chromoplasts. It 

 differs from carotin in being soluble in alcohol, and in being 

 deposited in amorphous and resin-like masses on the evapora- 

 tion of its solvent. It is but little soluble in ether and benzine. 

 Some varieties of xanthine are soluble in water while others are 

 not. It becomes green and then blue when treated with sulphuric 

 acid, and with potassium iodide-iodine it is colored green. 



