102 THE CARBOHYDRATES 



and amylo-dextrin occur. On the other hand, the ordinary 

 grains which are coloured blue with iodine, are made up almost 

 entirely of sphaero-crystals of amylose arranged in layers. 



According to Kraemer,* the starch grains of the potato are 

 composed of colloid and crystalloid substances arranged in 

 lamellae which are distinct and separate one from the other. 

 At the point of origin of growth, the hilum, and in the alter- 

 nate lamellae, the colloid preponderates and is associated with 

 the crystalloid cellulose ; in the other lamellae the crystalloid 

 granulose is in the greater proportion. He also states that 

 the peripheral layer is elastic and porous, and may be an an- 

 hydride of cellulose. Dennison also has expressed the view 

 that the outer layer of the grain is different from the more in- 

 ternal parts, and may be a carbohydrate not fully polymerized 

 to starch. 



The view that both crystalloid and colloid materials occur 

 in the starch grain is held by many ; in addition to those re- 

 ferred to above, Czapek may be mentioned ; it is, however, 

 not universally held, Fischer,f who believes that the grain is 

 composed of colloid substances, being a dissentient. 



Action of Acids on Starch. 



The action of acids on starch varies according to the 

 strength of the acid, the duration of the action, and the tem- 

 perature of the experiment. To complicate matters, there are 

 considerable divergences in regard to the interpretation of the 

 results obtained by the different workers. As an illustration 

 of the very different effects which may be produced under 

 different conditions, the following experiments may be 

 quoted. 



By acting on starch at the ordinary temperature with 

 12 per cent commercial hydrochloric acid for twenty-four 

 hours, Brown and Morris found that granules, while retaining 

 their external features, had acquired the power of dissolving in 

 hot water without the formation of paste. The addition of 

 alcohol to such a solution caused the immediate precipitation 

 of a white substance known as soluble starch, which is turned 

 blue by iodine, is strongly dextro-rotatory, [a] D = 202, and 



* Kraemer : " Bot. Gaz.," 1902, 34. 



t Fischer : " Beih. hot. Centr.," 1905, 181. 



