108 



PART II. THE ilNTIMATE STRUCTURE OF PLANTS. 



[ 25. 



cell-walls, where cuticularisation find lignification occur simul- 

 taneously. 



8. Mineral matters are also frequently deposited during growth 

 in considerable quantity in the cell-wall, particularly salts of lime 

 and silica ; they are usually intercalated between the solid organic 

 particles of the cell-wall, so that they cannot be directly detected, 

 but remain, after burning, as a skeleton which retains the form of 

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

 setaceae. Calcium oxalate sometimes occurs in a crystalline form 

 (Fig. 65.) Calcium carbonate is also frequently deposited in cell- 

 walls, as in certain Algae, (e.g. Acetabularia, Corallina, Jania, etc.) ; 

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





FIG. 65. Crystals of 

 calcium oxalate in the 

 wall of the bast-cells of 

 Cephalotaxus Fortunei. 

 (x 600 rafter Solms.) 



FIG. 66. A cystolith from the leaf of Celtis 

 Tala(x 200). 4 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. 



but most peculiarly in the cystoliths present in the epidermal cells 

 of the leaves of the Urticacese and Acanthacese : it may occur 

 either as granules or as crystals. 



A cystolith (Fig. 66 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 C0 2 , leaving the 

 cellulose basis (fl) which presents both striation and stratification. The 

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



25. Cell-Contents. The following are the principle cell- 

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

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



