86 VEGETABLE SUBSTANCES. 



[GLYCOGEN. 



This substance, which occurs in cells of fungi 

 in a semi-fluid, amorphous form, and more or less 

 intimately united with albuminoid structures, is 

 soluble in water as well as in acids and alkalies, but 

 insoluble in alcohol and ether. It does not reduce 

 Trommer's reagent, and gives no reaction with 

 osmic acid, Millon's reagent, or the salts of iron. 

 It may usually be distinguished from gums and 

 mucilage by not forming gelatinous masses in 

 water. 



The characteristic test for vegetable glycogen 

 is the red-brown or mahogany color it assumes 

 when treated with iodine in the presence of 

 water, the latter being essential, as in the cor- 

 responding reaction for starch. On heating the 

 preparation the color fades, reappearing when it 

 is cooled. 



Errera 1 recommends crushing the cells to be 

 tested in a drop of water under the cover-glass, 

 and immediately adding the iodine dissolved in 

 water containing a little iodide of potassium. 



Vigorous young plants of Phycomyces nitens 

 and Coprinus evanidus are recommended for this 

 test, though the reaction may be obtained with 



1 Errera : L'Epiplasme des Ascomycetes et le glycogene des V6getaux. 

 These presentee pour 1'obtention du grade de Docteur Agrege pres la 

 Faculte des Sciences de PUniversite de Bruxelles, 1882 ; Sur le glycogene 

 chez les Mucorinees. Bull. Ac. roy. de Belgique, Nov. 1882, 3 S6r., IV., 

 No. ii. 



