202 HISTOLOGY OF MEDICINAL PLANTS 



section, and the largest diamete.r is at the centre, from which 

 they taper gradually toward either end to a sharp point. 



Raphides occur in bundles, as in false unicorn root (Plate 79, 

 Figs, 6, A, B, and C), rarely as soHtary crystals. 



In ipecac root the crystals are usually solitary. In sar- 

 saparilla root, squill, etc., the raphides occur both in clusters, 

 part of bundle, or in bundles, and as soHtary crystals. 



In most drugs the crystals are entire; but in squills, where 

 the raphides are very large, they are broken. In phytolacca 

 (Plate 79, Fig. i) and in hydrangea the raphides are usually 

 broken, owing to the fact that these drugs contain large quan- 

 tities of fibres which break them up into fragments when the 

 drug is milled. 



There is the greatest possible variation in the size of raphides 

 in the same and in different drugs, but the larger forms are 

 constant in the same species. 



Raphides are deposited in parenchyma cells and in special 

 raphides sacs. These crystals are always surrounded with 

 mucilage. 



ROSETTE CRYSTALS 



Rosette crystals are compound crystals composed of an 

 aggregation of small crystals arranged in a radiating manner 

 around a central core. This core appears nearly black, and 

 the whole mass is nearly spherical. The free ends of the crystals 

 are sharp-pointed or blunt. 



Characteristic rosette crystals occur in frangula bark, spike- 

 nard root, wahoo stem, root bark, rhubarb, etc. (Plate 80, 

 Figs'. I, 2, 3, 4, 5, and 6). 



These crystals are very variable in size. This variation is 

 illustrated by the crystals of Plate 80. 



Usually there is a variation in size of the crystals occurring 

 in a given plant, but for each plant there is a more or less uni- 

 form variation. For instance, the largest rosette crystal occur- 

 ring in wahoo root bark (Plate 80, Fig. 5) is smaller than the 

 largest crystal occurring in rhubarb (Plate 80, Fig. 6), etc. 



The prisms forming the rosette crystals, hke all prisms, 

 decompose white light, with the result that rosette crystals 

 frequently appear variously colored. Rhubarb crystals, for 



