220 BOTANICAL MICROTECHNIQUE. 



appearance of vacuoles (Fig. 49, II, a\ because they have a 



lower refractive index than these 

 media. They may be best ob- 

 served by dissolving the funda- 

 mental mass of the protein-grain 

 and the crystalloids contained in it 

 with dilute, about i$, caustic potash 

 solution, from sections previously 

 deprived of their fat by alcohol or 

 ether-alcohol. There remain then 



FIG. 50. I, globoids, II, crystal- , , f > . t 



loids, of Berthoiietia exceisa ; in the space formerly occupied by 



III, protein-grain of Eleeis gui- , . 1111-1 



neensis ; IV, protein grains of the protein-gram Only the glODOlds 



Vitis vinifera ; g, globoid with . . . 



calcium oxalate crystal in the and ailV CalClUttl OXalate Cl'VStals 



middle. 



that may be present. To distin- 

 guish between these two constituents, polarized light may 

 be used. The globoids are amorphous and therefore iso- 

 tropic, while the oxalate crystals (cf. 392) are strongly 

 doubly refractive. 



For the same purpose, a dilute, about i#, acetic acid 

 may be used, in which the crystals are insoluble, while the 

 globoids are quickly dissolved by it. In concentrated acetic 

 acid the globoids are soluble with much greater difficulty. 



In a concentrated aqueous solution of sodium pliosphate 

 the globoids are completely soluble, according to Liidtke 

 (I, 79), even after treatment with corrosive sublimate. But 

 this solution requires several hours, and the larger globoids, 

 like those from the seed of Vitis vinifera, show during solu- 

 tion an evident stratification which gradually penetrates from 

 without inwards. Liidtke also observed similar stratifica- 

 tions when he allowed dilute caustic potash or lime-water to 

 act for a long time on the globoids. 



It may be remarked here that the globoids are also dis- 

 solved by picric acid. The protein-grains, however, preserve 

 their original form completely in this fluid, and cavities may 

 be seen in them which have exactly the forms of the dis- 

 solved globoids. 



390. Pfeffer (I, 472) used the following reactions for the 

 recognition of the chemical composition of the globoids. 



