1. Cactus grandiflorus (Cereus grandiflorus [L.], Britton and Rose).
2. Hemlock bark (Tsuga canadensis [L.], Carr.).
3. Krameria root (Krameria triandra, Ruiz and Pav.).
4. Soapbark (Quillaja saponaria, Molina).
PLATE 84
Solitary Crystals
1. Coca leaf (Erythroxylon coca, Lamarck).
2. Xanthoxylum bark (Zanthoxylum americanum, Miller).
3. Elm bark (Ulmus fulva, Michaux).
4. Spanish licorice root (Glycyrrhiza glabra, L.).
5. White oak bark (Quercus alba, L.).
Cubes occur in senna, cascara sagrada, frangula, white pine, tamarac (Plate 85), quassia, uva-ursi, quebracho, and in wild cherry (Plate 86).
The crystals of morea nutgalls (Plate 82, Fig. 3) are octahedrons, and they resemble the crystals of calcium oxalate found in urinary sediments.
While studying the prisms, focus first on the upper surface and then down to the under surface in order to observe the forms accurately.
There are several plants in which more than one form of crystal occur. Rosette crystals and prisms are associated, for instance, in cascara sagrada, frangula, condurango, dogwood, and pleurisy root (Plate 87, Figs. 1, 2, 3, 4, and 5).
An important factor to be kept in mind in studying crystals is the number—whether abundant, as in rhubarb, or sparingly present, as in mandrake, etc. Variation in the number of crystals is not uncommon, even in different parts of the same plants. In wahoo stem bark, for instance, there are several times as many rosette crystals as there are in the root bark.
Crystals of calcium oxalate are freely soluble in dilute hydrochloric acid without effervescence; but they are insoluble in acetic acid and in sodium and potassium hydroxide solutions. With sulphuric acid they form crystals of calcium sulphate.