SPECIAL METHODS. 229 



Amylodextrine is almost insoluble in cold water, but is 

 easily dissolved by water at 60 C., and is not thrown down 

 from such a solution on cooling. But, on evaporation or 

 freezing, amylodextrine separates from its solution in the 

 form of characteristic crystalline disks, the so-called " disco- 

 crystals " (cf. W. Naegeli I, and Naegeli and Schwendener 



I, 359)- 



408. Amylodextrine also arises as an intermediate prod- 

 uct in the transformation of starch into dextrine and malt- 

 ose. If starch-grains are heated for some time at 50 C. in 

 the salivary ferment, they lose, usually after a few hours, 

 the power to become blue with iodine, and take at first a 

 violet, then a wine-red, and finally a pure yellow color, ac- 

 cording to the length of time the ferment has acted. Nev- 

 ertheless the grains which remain, the so-called " starch- 

 skeletons," still have the original form of the starch-grains 

 and often show distinct stratification. These starch-skele- 

 tons, consisting of amylodextrine, may also be obtained by 

 the action of dilute hydrochloric or sulphuric acid for years 

 upon unchanged starch-grains. 



409. But the solution of starch within the living plant 

 takes place in another way. As has lately been described 

 in detail by Krabbe (I), either there occurs a regular solu- 

 tion from without inwards, or local corrosions are formed in 

 the shape of pit- or crater-shaped depressions. In small 

 grains pore-canals are often formed, which may penetrate 

 to the interior of the grain and lead to the formation of a 

 central cavity. 



Diastase acts in a similar manner. It may be prepared 

 by the solution of malt extract in water. A very useful 'fer- 

 ment-containing fluid may be prepared by adding to the 

 aqueous solution of commercial diastase about .05$ of citric 

 acid (cf. Detmer I, 197). 



410. Finally there may be mentioned here a substance 

 commonly termed soluble or amorphous starch, which agrees 

 with true starch in being colored blue or violet to red by 

 iodine solutions. But it is soluble in water and occurs only 

 in the cell-sap of the epidermal cells of a few plants ; for ex- 



