286 



VEGETABLE PHYSIOLOGY 



certain Saxifrages. In these it aids in the formation of a 

 subsidiary water-absorbing apparatus as will be mentioned 

 in a subsequent chapter. 



In most cases the materials which we are discussing 

 are not thrown off from the plant, but are removed to parts 

 which are not concerned in the vital processes to any very 

 great extent. Etherial oils are found deposited in special 

 cavities in leaves, stems, and other parts (fig. 130). 

 Mineral matters are often deposited in the substance of 

 cell-walls. The oxalate of calcium occurs frequently in 



FIG. 130. DEVELOPMENT OF LYSIGENOUS GLAND IN 

 STEM OF Hypericum. THE FOUR FIGURES REPRE- 

 SENT SUCCESSIVE STAGES. X 250. 



FIG. 131. CRYS- 

 TALS OF CALCIUM 

 OXALATE IN 

 WALL OF CELL 

 OF THE BAST OF 

 Ephedra. 



this situation (fig. 131). In other cases it is deposited in 

 special cells, where it forms clusters of crystals of cha- 

 racteristic shape (fig. 132, A, B). In these cases the cluster 

 of crystals is usually invested by a delicate skin derived 

 from the protoplasm, thus shutting it completely off from 

 any participation in the metabolism of the cell in which it 

 lies. 



Carbonate of calcium may also be deposited in the 

 substance of the cell- wall, or of protrusions from it, as 

 in the cystoliths of Ficus, Urtica, and other plants (fig. 

 133). 



