MINERALIZATION. 39 



the cell-cavity, and not in the cell-wall. Sulphuric acid and 

 chromic acid, even when concentrated, produce little effect on 

 cutinized membranes, beyond removing traces of cellulose pres- 

 ent in the cell-wall. The latter acid, however, increases the 

 transparency of cutinized membranes, especially after prolonged 

 action. 



161. Potassic hydrate softens such membranes and colors 

 them yellow ; when heated it breaks them into a granular mass 

 which may be removed by careful washing. Cautiously heated 

 with Schulze's macerating liquid, they disintegrate into granules 

 of eerie acid. a substance which dissolves in alcohol, ether, and 

 benzol. Several of the coal-tar colors stain the cutinized por- 

 tions of cell-walls very deeply ; if the specimen thus colored is 

 placed in absolute alcohol, the cutinized parts alone remain 

 colored. 1 Two points relative to the cutinization of epidermal 

 cells may be noted : (1 ) the cutin may take on the form of lay- 

 ers, often numerous and conspicuous ; (2) there ma}- be a con- 

 siderable irregularity in the outline of the deposits, sometimes 

 as folds, hooks, and the like, which do not strictly conform to 

 the cellulose wall on which the)- arise. 



162. Mineralization of the cell-wall. Although all cell-walls, 

 even the most delicate, can be shown to contain traces of inor- 

 ganic matter, it is only in a few special cases that such substances 

 appear in a form to be noticed under the microscope. Minerali- 

 zation of the wall ma}- be general or local, may depend upon 

 the presence of crystals or of amorphous deposits, and these may 

 consist of silicic acid or of calcium salts. 



163. General mineralization of the wall depends most fre- 

 quently on silicic acid, and may be best demonstrated by first 

 boiling the specimen in nitric acid, drying, heating to redness on 

 platinum-foil, and. lastly, treating again with nitric acid. The 

 silicic acid remains behind as a delicate skeleton which copies in 

 all particulars the contour of the wall of which it formed a part. 

 Fine examples are afforded by the harder grasses. 2 



Calcium salts may exist in crystalline or amorphous form, and 

 may be distinguished by the tests to be given for them under 

 the section on " Crystals." That in some cases they constitute 

 an integrant part of the wall itself admits of no question. 



164. Iq the cells of many plants, especially Urticacese, pedi- 

 cellated concretions occur, which, on superficial examination, 



1 Olivier: Bull. Soc. bot. de Fr., 1880, p. 234. 



a Tabashetr consists of the siliceous substances which occur in the joints 

 of bamboo in large quantities. 



