PART II. ANATOMY AND HISTOLOGY. 



[24 



the cell. Silica is present in the stems of Grasses and of Equi- 

 setacese. Calcium oxalate sometimes occurs in a crystalline form 

 (Fig. 51.) Calcium carbonate is also frequently deposited in cell- 

 walls, as in certain Algse (e.g. Ace tabu laria, Coralline^ Jama, etc.) ; 

 also in hairs of some of the higher plants (e.g. many Boraginacese) ; 

 but most peculiarly in the cystoliths present in the epidermal cells 

 of the leaves of Ficus clastica, and of the Urticacese and Acan- 

 thacese : it may occur either as granules or as crystals. 



A cystolith (Fig. 52 A) consists of a basis of cellulose incrusted with 

 calcium carbonate. On treating a section, containing a cystolith, with 

 acid, the calcium carbonate is dissolved with evolution of bubbles of CO 2 , 

 leaving the cellulose basis (B) which presents both striation and strati- 

 fication. The cellulose basis is, in fact, a local thickening of the cell-wall. 



Fio.] 61. Crystals o 

 calcium oxalate in the 

 wall of the bast-cells of 

 Cephalotaxut Fortune*. 

 (x600:afterSolms.) 



FIG. 62. A cystolith from the leaf of Celtis 

 Tala ( x 200) . A Normal condition ; c cysto- 

 lith ; e epidermal layer; p palisade-tissue. 

 B The cystolith after treatment with hydro- 

 chloric acid which has dissolved the calcium 

 carbonate, leaving the stratified cellulose 

 basis. 



24. Cell-Contents. The following are the principal cell- 

 contents which are not protoplasmic and are, in fact, not living : 

 they are moreover not universally present in cells, but are con- 

 fined to special cells, and frequently to special plants: starcL- 

 grams ; fatsj proteid grains and crystalloids ; mineral crystals ; 

 the cell-sap, and the substances dissolved in it. 



a. Mm-cli-grains are small solid granules of various shape- 

 rounded, oval, lenticular, etc. consisting of starch_with a certain 

 amount of water and a small proportion of incombustible ash. 

 They are specially abundant in those parts of plants which serve 



