8O VEGETABLE SUBSTANCES. 



the reagents used for detecting pure cellulose. 1 

 There is, therefore, no reason for considering 

 "metacellulose " as a distinct substance. It should 

 be looked upon simply as a modification similar to 

 that of wood and bark. 



The paraphyses and asci of lichens are, as a 

 rule, colored blue by iodine, as are the hyphae of 

 the medullary layer in some cases. This is to be 

 attributed to the presence of lichenin, a sub- 

 stance characteristic of these plants. 



PROTEIN SUBSTANCES 



Are easily characterized by the brown color which 

 is imparted to them by iodine, the rosy red which 

 they assume when acted upon by Millon's reagent, 

 especially after gentle warming, and the yellow 

 which is produced by nitric acid 2 either alone or 

 in combination with ammonia. After lying for 

 about twelve hours in corrosive sublimate in 

 alcohol, they form a compound, insoluble in water, 

 which is especially interesting in preparations of 

 aleuron grains. Protein compounds become violet 

 when treated with Trommer's reagent ; sugar and 

 sulphuric acid (Raspail's reagent, 1833) color them 

 red. The imbibition and condensation of different 

 coloring matters, e. g. cochineal, carmine, a solu- 



1 Van Tieghem: Traite de botanique, 1882, p. 569. 



2 Discovered in 1686 [?] by Glauber (Explicatio miraculi mundi). 

 Mulder has given the yellow compound the name " Xanthoproteic acid" 



