344 MICROCHEMISTRY OF PLANT PRODUCTS 



under the coverglass, crystals of dulcite will be deposited in the 

 form of long, branched prisms or needles radiating from a com- 

 mon center. They are distinguished from crystals of potassium 

 nitrate by dissolving in diphenylamine and sulphuric acid with- 

 out coloration, and by being insoluble in a concentrated solution 

 of dulcite. 



Elaioplasts. These are rounded or irregularly polygonal, 

 more or less granular bodies, consisting of a protoplasmic stroma 

 and inclosed oil, which occur closely applied to the nucleus in 

 the epidermal cells of many monocotyledonous and some dicoty- 

 ledonous plants. In old cells the elaioplasts have the appearance 

 of a sponge saturated with oil. The oil in the elaioplast of Or- 

 nithogalum umbellatum may be almost instantly dissolved by 

 means of alcohol. The elaioplasts may be fixed and stained at 

 the same time by treating sections containing them with a dilute 

 solution of alcannin in i per cent, acetic or formic acid. The 

 acid fixes the protoplasmic stroma, while the alcannin stains the 

 oil a beautiful red. The fixing and staining process should be 

 complete in five minutes. If desired, the sections may be double- 

 stained by transferring them from the alcannin to a solution of 

 iodine-green and glycerine, after which they may be mounted in 

 glycerine-jelly. The sections may also be stained in a mixture 

 of a dilute solution of alcannin and a solution of iodine-green in 

 ^o per cent, alcohol and i per cent, acetic acid. 



Emulsin. This is a glucoside-splitting ferment which occurs 

 in certain cells of the almond and of the bundle-sheath of the 

 leaves of Prunus laurocerasus and in other Rosaceae, where it 

 splits up the glucoside amygdalin into glucose, hydrocyanic acid 

 and benzaldehyde. When sections are treated with Millon's 

 reagent, the cells containing emulsin take on an orange-red color, 

 while the surrounding cells are colored a pale rose-red. A solu- 

 tion of copper sulphate and caustic potash produces a violet 

 color in the emulsin-bearing cells. 



Ethereal Oils. Ethereal oils are distinguished from fatty oils 

 in that they may be distilled from plants along with vapor of 

 water, and are soluble in glacial acetic acid, and an aqueous 



