25.] 



CHAPTER I. THE CELL. 



113 



,/r 



FIG. 71. Crystals of calcium oxalate in the cells of the 

 petiole of a Begonia ( x 200). fc Solitary crystals ; dr cluster. 



pericarp and testa of some plants (e.g. Celtis australis, Lithospermum 

 ojficinale, Cerinthe glabra). 



In all other cases the crystals consist of calcium oxalate, which 

 crystallises in two systems according to the proportion of water 

 which it contains ; 

 to the one system, 

 the quadratic, be- 

 long the octahedra 

 (Fig. 71 k) ; to the 

 other, the clino- 

 rhombic, belong 

 the acicular crys- 

 tals, distinguished 

 as raphides, which 

 occur in bundles 

 in the cells of Mo- 

 nocotyledons more 

 especially (Fig. 72), 

 and are generally 

 associated with mu- 

 cilage in the cell. 



It sometimes happens that the crystal, or group of crystals, be- 

 comes surrounded by a layer of cellulose attached to the wall at 

 one or more points (e.g. leaf of Citrus vulyaria, pith of Kerria 

 japonica). 



e. The Cell-Sap saturates the cell-wall, the protoplasm, in fact 

 the whole organ- 

 ised structure of 

 the cell ; it also 

 fills the vacuole, 

 when present, in 

 the cytoplasm. It 

 is a watery solution 

 of the most various 

 substances. In all 

 cases is holds salts 

 in solution, con- 

 sisting mainly of alkaline bases in combination either with inor- 

 ganic acids, such as nitric, phosphoric, and sulphuric acid, or with 

 organic acids, such as malic (e.g. apple and other fruits), citric 

 (lemon, etc.), and others. It frequently contains tannin, and 



V. s. B. I 



FIG. 72. Raphides (fc) in a cell of a bulb-scale of Urginea 



maritima (x200) ' 



