i86 



A TEXT-BOOK OF BOTANY. 



carpus, pimenta, rheum, rumex, senna, stillingia, stramonii folia,, 

 viburnum opulus, and viburnum prunifolium. 



IV. RAPHIDES are groups of needle-shaped crystals, especially 

 prevalent in Monocotyledons (Fig. 107, B). They have been mis- 



FIG. 107. Forms of calcium oxalate crystals: A, transverse section of rheum show- 

 ing rosette aggregates of calcium oxalate in three of the cells and starch grains in some of 

 the others; B, longitudinal section of scilla showing raphides; C, longitudinal section of 

 quillaja showing large monoclinic prisms of calcium oxalate and also some starch grains; 

 D, transverse section of belladonna root showing one cell filled with sphenoidal micro-crys- 

 tals, the remaining cells containing starch. 



taken by several observers for calcium phosphate. Calcium phos- 

 phate, however, occurs in plants either in solution or in com- 

 bination with protein substance. The cells containing raphides 

 are long, thin-walled and contain, sooner or later, a mucilage, 



