GLOBOIDS — GLUCOSE 347 



This process should be repeated several times, until the deposit 

 of Turnbull's blue is sufficiently dense to cause the sheaths to 

 stand out quite sharply. By this method very instructive double- 

 stains may be achieved with algae which have been growing in 

 a dilute solution of Congo-red (see under this head in the last 

 chapter), which stains the cell- walls, but not the gelatinous 

 sheaths. See also in the last chapter under India Ink. 



Globoids. — The globoids found in aleurone grains consist of 

 a double phosphate of calcium and magnesium, which is insoluble 

 in alcohol and dilute potassium hydrate, but is soluble in dilute 

 mineral acids and in acetic, oxalic, and tartaric acids. In an 

 ammoniacal solution of ammonium phosphate the globoids are 

 replaced by groups of crystals of ammonium-magnesium 

 phosphate. Treated with ammonium oxalate, they become 

 replaced by crystals of calcium oxalate. The globoids may be 

 isolated to a certain extent by extracting the oil from sections of 

 endosperm containing them by means of alcohol or alcohol and 

 ether, and then dissolving the ground substance and crystalloid 

 by means of a i per cent, potassium hydrate. If crystals of cal- 

 cium oxalate are present along with the globoids, they may be 

 distinguished by means of the polarizer, since they are doubly 

 refractive, while the globoids are not. 



Glucose, CgHjjOg. — This carbohydrate occurs in sweet fruits 

 and in the leaves and other members of plants, being one of the 

 most common forms in which carbohydrates circulate within the 

 plant. The warty crystals of glucose which are deposited from 

 aqueous and alcoholic solutions at low temperatures melt at 86°, 

 and become free from water at 110° C. At from 30 to 35° C. 

 glucose crystallizes from concentrated solutions in water, ethyl- 

 and methyl-alcohol in the form of hard crusts, which melt at 146° 

 C. The presence of glucose may be easily demonstrated in the 

 fruit of the pear, for instance, and in the leaves of Balsamina, 

 or other rather translucent leaves which have been cut from the 

 parent plant and kept fresh under a bell-jar for several days. 

 Pieces of the flesh of a ripe pear may be put into a test-tube with 

 Fehling's solution and brought to a boil, when a reddish precipi- 



