174 BOTANY AND I'liARAl ACUUA'USY. 



the crystalloids, globoids and calcium oxalate. On adding a 

 o.i to I per cent, solution of either sodium or potassium hydrate, 

 the crystalloids dissolve, the globoids and calcium oxalate crystals 

 remaining unaffected. The globoids may be dissolved by the 

 use of a I per cent, acetic acid solution, or concentrated solu- 

 tions of anmionium sulphate or monopotassium phosphate. The 

 calcium oxalate remaining may then be treated with hydrochloric 

 acid in the usual way. 



IT AxMORPHOUS .SUBSTANCES. 



Cystoliths. Occasionally cells are found among the paren 

 chyma or in the inner row of the epidermal cells on the upper side 

 of the leaf, the walls of which form an inward protrusion intn tlie 

 cell and l)ecome impregnated with and encrusted by calcium car- 

 l)onate, giving rise to more or less stalked bodies known as cysto- 

 liths (Fig. 221). The calcium carbonate dissolves on the 

 application of acetic acid, leaving a core which responds to the 

 tests for cellulose. Cystoliths are not of common occurrence, 

 being found with but few exceptions in the two families Acan- 

 thace^e and Moraceae, and in a few species of the Cucurbitacese. 

 in the leaves of the cultivated rub])er plant the cystoliths have 

 long stalks, whereas in cannabis indica (Fig. 279), they are 

 sessile. 



Tannin and Tannoids. Tannins are astringent principles 

 which belong to the class of phenol acids and give blue or green 

 precipitates with iron salts. The tannoids, in addition, precipitate 

 albuminous compounds, and when applied to animal hides con- 

 vert them into leather. These principles are widely distributed, 

 occurring dissolved in the cell-sap, in parenchyma cells or 

 in distinct reservoirs or vessels, and vary in amount from 

 T per cent, or less to as high as 70 per cent, in Chinese galls. 

 Tannin may be precipitated in the plant cells by copper acetate. 



Mucilages and Gums. By the terms mucilages and gums 

 are meant those substances which are soluble in water, or swell 

 very perceptibly in it, and which, upon the addition of alcohol, 

 are precipitated in the form of a more or less amorphous or gran- 

 ular mass. Mucilage originates in the plant as a cell-content, or 

 as a modification of the wall. In the former case it arises as a 



