BOTANICAL MICRO7^ECHNIQUE. 



acetic acid, and amyl ale ohol, and in dissolving in concentrated 

 -sulphuric acid with a saffron-yellow color ; while chryso- 

 phanic acid is very slightly soluble in the first three reagents 

 and dissolves in sulphuric acid with a rose-red color. Ac- 

 cording to Fr. Schwarz(II, 251), emodin is also distinguished 

 from chrysophanic acid by dissolving in ammonium carbonate 

 Avith a red color, while the latter remains unchanged in this 

 reagent. 



c. Chrysophanic Acid, C 14 H B O 3 .CH,.(OH) 3 . 



141. Chrysophanic acid has been observed especially in 

 the lichen Physcia parietina and in the roots of various Poly- 

 gonacece. In the latter it occurs, according to Borscow (I), 

 in the form of yellow granules imbedded in the cytoplasm. 

 But in Physcia it is in the form of crystalline granules ad- 

 hering to the membrane, as Fr. Schwarz (II, 262) has shown, 

 in opposition to Borscow (I). These are very small and can 

 be plainly recognized only by strong magnification. In 

 polarized light they glisten brightly with crossed nicols. 

 They are characterized by the deep crimson color which 

 they take with caustic potash or ammonia ; while lime and 

 baryta waters color them dark red, without dissolving them 

 (see also 140). 



5. Hydrocarbons, (C, H, 8 )x. 



142. A large group of various vegetable substances is 

 included by Beilstein (III, 279) under this title. They repre- 

 sent either terpenes of the composition C 10 H 16 or polymeri- 

 zation products of these, or at least are very nearly related 

 to them. Beside the true terpenes there are included here 

 especially the ethereal oils, caoutchouc and gutta percha, 

 the resins and balsams. The chemical constitution of some 

 of these compounds has been very little studied, and doubt- 

 less many of the substances placed here will in time be 

 transferred to other parts of the natural system, especially 

 many of the so-called ethereal oils. Thus, the chief constit- 

 uent of the so-called ethereal oil of the species of A Ilium, 



