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= 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, spikenard root, wahoo stem, root bark, rhubarb, etc. (Plate 80, Figs. 1, 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 uniform variation. For instance, the largest rosette crystal occurring in wahoo root bark (Plate 80, Fig. 5) is smaller than the largest crystal occurring in rhubarb (Plate 80, Fig. 6), etc.
1. Phytolacca root (_Phytolacca americana_, L.). 2. Squills (_Urginea maritima_ [L.] Baker). 3. Hydrangea root (_Hydrangea arborescens_, L.). 4. Convallaria (_Convallaria majalis_, L.). 5. Carthagean ipecac (_Cephælis acuminata_ Karst.) 6. Bundle of raphides from false unicorn root.
_A._ Bundle surrounded with mucilage. _B._ Mucilage expanded and partially dissolved. _C._ Bundle free of mucilage.]
1. Frangula bark (_Rhamnus frangula_, L.). 2. White oak bark (_Quercus alba_, L.). 3. Spikenard root (_Aralia racemosa_, L.). 4. Wahoo stem bark (_Euonymus atropurpureus_, Jacq.). 5. Wahoo root bark (_Euonymus atropurpureus_, Jacq.). 6. Rhubarb (_Rheum officinale_, Baill.).]
The prisms forming the rosette crystals, like all prisms, decompose white light, with the result that rosette crystals frequently appear variously colored. Rhubarb crystals, for instance, are blue or violet. Most of the smaller rosette crystals, however, appear grayish white with a darker-colored centre.
Rosette crystals occur in parenchyma cells (Plate 81, Fig. 4) and in medullary rays (Plate 81, Fig. 3).
=Solitary crystals= are the most variable of all the forms of calcium oxalate. They usually occur in crystal cells associated with bast fibres and stone cells, less frequently in stone cells (Plate 33, Fig. 2). There are many different and characteristic forms of prisms. The more common are: