220 THE CARBOHYDRATES. 



3. Colloid Polysaccharides. 



If we exclude the not well known trisaccharides and the tetrasaccharide 

 stachyose, this group includes a great number of very complex carbo- 

 hydrates which occur only in the amorphous condition, or at least not 

 as crystals in the ordinary sense. Unlike the bodies belonging to the 

 other groups, these have no sweet taste. Some are soluble in water, 

 while others swell up therein, especially in warm water, and finally 

 some are neither dissolved nor visibly changed. Polysaccharides are 

 ultimately converted into monosaccharides by hydrolytic cleavage. 



The polysaccharides are ordinarily divided into the following groups: 

 starches with the dextrins, plant gums and mucilages, and the celluloses. 



Starch Group. 



Starch, AMYLUM (CeHioC^x. This substance occurs in the plant 

 kingdom very extensively distributed in the different parts of the plant, 

 especially as reserve food in the seed, roots, tubers, and trunks. 



Starch is a white, odorless, and tasteless powder, consisting of small 

 granules which have a stratified structure and different shape and size 

 in different plants. Starch is considered insoluble in cold water. The 

 grains swell up in warm water and burst, yielding a paste. 



According to the ordinary opinion the starch granules consist of two 

 different substances, STARCH GRANULOSE and STARCH CELLULOSE (v. 

 NAGELI), the first of which turns blue with iodine and forms the chief 

 part of the granule. According to MAQUENNE and Roux 1 this is 

 not the fact. According to them the starch granule consists of two 

 constituents, of which the first, amylose, forms the chief mass (80-85 

 per cent) and the other, amylopectin, forms only 15-20 per cent of the 

 granule. Amylopectin is not identical with v. NAGELI' s starch cellulose, 

 and the above investigators consider starch cellulose as only an insoluble 

 form of amylose. The amylose can occur in two forms. One, which is 

 soluble, is colored blue by iodine and is immediately transformed into 

 sugar by malt. The other is a solid substance, which is not colored 

 with iodine and resists the action of malt infusion. One modification 

 can be transformed into the other. 



In the paste, besides amylopectin, we also have soluble amylose, and 

 this can, by a process called rttrogradation by MAQUENNE and Roux, be 

 transformed into the solid modification, into " artificial starch." This 

 solid form occurs in the starch granule, and is identical with v. NAGELI'S 

 starch cellulose. As the starch granules are directly colored blue by 



*v. Nageli, Botan. MitteiL, 1863; Maquenne and Roux, Compt. rend., 138, 140, 

 142, 146, and Bull. Soc. chim. de Paris (3), 33 and 35. 



