36 PROXIMATE CONSTITUENTS OF PLANTS 



soluble starch cellulose formed from the cell walls, 

 which have burst under the action of heat and liberated 

 the soluble starch. 



(ii.) The boiled solution is filtered, and alcohol 

 added to the clear filtrate. A precipitation of starch 

 granulose takes place. 



(iii.) A drop of iodine in potassium-iodide solution 

 is added to the boiled filtered solution, and also to a 

 portion of the original paste. The granulose alone 

 gives the characteristic blue coloration of starch iodide. 

 The coloration is discharged on heating to 80° C, but 

 returns on cooling, becoming deeper the lower the 

 temperature. 



(iv.) A little starch paste is boiled for a quarter of 

 an hour with dilute HCl, whereby it is hydrolysed, 

 first to dextrin, then to glucose, the presence of which 

 can be demonstrated by addition of Fehling's solution, 

 and boiling. 



(C6H,o05)„+;.Hp = ;.CeH,A. 

 (v.) Starch is hydrolysed to maltose in a similar 

 way by the action of diastase (see 34, p. 55). 



CHAPTER III 

 Proximate Constituents of Vlki^ts— continued 



{e) The Alkaloids. 



The alkaloids are nitrogenous organic substances occurring in 

 small proportions in certain plants, generally of the dicotyledonous 

 family. Their importance lies in the fact that they are bodies 

 of great therapeutical value, owing to their marked action on 

 certain nerve centres. They are generally powerful poisons, when 

 taken in any except minute doses. 



