PLANT PRODUCTS 563 



ready demonstration of asparagin, tubers of dahlia may be employed. Rather 

 thick sections are cut from a tuber while the razor is kept dry and transferred to 

 a few drops of alcohol on a glass slide and covered with a cover-glass. On the 

 evaporation of the alcohol crystals of asparagin in the form of rhombic plates are 

 deposited on the cover-glass and slide. To determine whether the crystals are 

 asparagin, they are treated with a few drops of a saturated solution of asparagin, 

 which must be entirely saturated and of the same temperature as the preparation. 

 If the crystals are asparagin, instead of being dissolved they will increase in size, 

 while other substances than asparagin will dissolve in the saturated asparagin solu- 

 tion just as they would in water. It is characteristic of asparagin that if the crys- 

 tals are heated to iooC., they lose their water of crystallization and appear like 

 bright droplets of oil. At 200 asparagin becomes decomposed and forms frothy 

 brown droplets which are no longer soluble in water. 



Atropine, CnH^NOa. In sections containing atropine a solution of potassium 

 iodide-iodine produces a brown precipitate, while phosphomolybdic acid produces a 

 yellow precipitate. 



Bassorin. Gum tragacanth, obtained from certain cells of the pith and medul- 

 lary rays of several species of Astragalus. Swells strongly in water, but does not 

 go into complete solution. Is not colored either by iodine or chloriodide of zinc. 



Berberine, C2oHi7NO4 + 4^H 2 O. This occurs in the young parenchymatous 

 tissue, and in the older xylem portions of Berberis vulgaris. With potassium iodide- 

 iodine it forms a reddish-brown precipitate which, by treatment with alcoholic 

 potassium iodide-iodine, becomes changed into tubular or hair-like forms which have 

 a brownish or iridescent green color. Ammonium and nitric acid impart to ber- 

 berine a reddish-brown color. A solution of potassium bichromate or potassium 

 iodide in 50 per cent, sulphuric acid produces, with berberine, an intense purplish- 

 red color. One part of nitric acid mixed with 100 parts of water added to sections 

 containing berberine will produce clustered acicular crystals of berberine nitrate 

 within the berberine-bearing cells. 



Betulin. This occurs in the form of fine granules in the thinner walled cork 

 cells of birch bark. In order that it may be studied to good advantage under the 

 microscope, the air should be . pumped from sections immersed in water, and then 

 the sections should be examined in water under the microscope. Betulin is in- 

 soluble in water, but is soluble in alcohol. It is strongly antiseptic, and protects 

 birch bark against the attacks of lower organisms. 



Betuloretic Acid, CseHeeOs. This is secreted by the glandular hairs on the 

 leaves of Betula alba. It is obtained from the thick, pale yellow secretion by 

 successive solution in boiling alcohol, ether, and an aqueous solution of sodium 

 carbonate. It is colored a beautiful red by concentrated sulphuric acid. 



Brucine, C23H 2 6N 2 O4 + 4H 2 O. Brucine occurs in the seeds of various species 

 of strychnos. Ammonium vanadate in sulphuric acid gives with brucine a yellow- 

 ish-red color. When sections containing brucine are treated with a mixture of 

 nitric and hydrochloric acids, the cell-contents are colored a reddish-orange, 

 which merges into yellow. 



Caffeine, CsHioN^ + H 2 O. When sections containing caffeine (theine, 

 methyl-theobromine, trimethyl-xanthin) are treated with a drop of concentrated 

 hydrochloric acid, and then after a minute with a drop of a 3 per cent, gold chloride 

 solution, somewhat slender, yellowish, silken crystals of a double chloride of gold 

 and caffeine begin to be formed on the evaporation of the reagent. However, 

 theobromine forms quite similar crystals when treated as above. Another method 

 .for the detection of caffeine is to place sections in a few drops of water and heat 



