178 BOTANY AND PHARMACOGNOSY. 



The mucilages are further distinguished by their behavior 

 toward reagents; those which are colored blue by chlor-zinc- 

 iodide, and are soluble in ammoniacal solution of cupric oxide, 

 are known as cellulose mucilages. To this class belong the mu- 

 cilages of the tuber of salep and the seeds of cydonium. Most of 

 the other mucilages, particularly the pectose-mucilages, are col- 

 ored by alcoholic and glycerin solutions of the basic aniline dyes. 



Mucilage which occurs in cells containing raphides is stained 

 by corallin, which is not usually the case with the other mucilages. 



Oils, resins and their associated products, like the mucil- 

 ages and tannins, are formed in the plant either as a result of the 

 activities of the protoplasm, or by reason of abnormal or patho- 

 logical changes in some of the constituents of the cell. The oils 

 may be divided into two principal classes, namely, the reserve or 

 fixed oils, which are more or less intimately associated with the 

 protoplasm in fruits and seeds ; and the volatile oils which occur 

 in special secretion cells or special canals. The former are large 

 parenchyma cells, the walls of which are not infrequently suber- 

 ized, and are found in rhizomes, as of calamus (Fig. loi, B) and 

 ginger; in barks, as sassafras (Fig. 236) and cascarilla; in fruits, 

 as capsicum, cubeba (Fig. 250), piper and cardamomum. Oil 

 secretion canals are cavities formed either as a result of the en- 

 largement of the intercellular spaces, due to the separation of the 

 cells, or as a result of the disintegration of a number of cells. The 

 former are spoken of as being schizogenous in origin, and the 

 latter as lysigenous. These terms are also used to designate simi- 

 lar reservoirs holding mucilage, gum-resins and other products. 

 The schizogenous reservoirs are of more common occurrence, and 

 are found in inula, arnica rhizome, caryophyllus and the umbel- 

 liferous fruits (Figs. 244-248) and various leaves, as eucalyptus 

 and pilocarpus (Fig. 257). The volatile oils are characteristic of 

 some of the largest families of plants, as the Compositse, Labiatas, 

 Rutaceae and Umbelliferse. 



The oils, both fixed and volatile, are insoluble, or nearly so, 

 in water; but are soluble in ether, carbon disulphide, chloroform, 

 benzin, benzol and acetone. Most of the volatile oils and a few 

 of the fixed oils are more or less soluble in alcohol. They are col- 

 ored brownish or brownish-black with osmic acid. The volatile 



