0BYSTAL8. 



61 



(a) In studying plant-crystals it is only necessary in most cases 

 to make thin longitudinal sections, and to mount in the usual way 

 in water. 



(6) The calcium carbonate crystals may Le distinguished from those 

 of calcium oxalate by treatment with hydrochloric acid, which dissolves 

 both, the former with effervescence, the latter with none. Under 

 treatment with acetic acid the calcium carbonate crystals dissolve (with 

 efEervescence, of course), while those of calcium oxalate do not dissolve. 



(c) Acicular crystals, or raphides, may be best obtained from the 

 Evening Primrose, EpiloMum, Fuchsia, and other Onajrraceae, also from 

 tlie Balsam (Impatieiis Bid>.amiiia), Garden Rhubarb, and the new 

 growths of the Virginia Creeper, and the grape-vine. 



Raphides may also be obtained from some of the Monocotyledons 

 with equal ease, e.g., Tradescantia, Indian turnip (Arismma), Calla, 

 Narcissus, Lily-of-the- Valley, etc. 



((f) The other crystal forms are obtainable from the bark of the lo- 

 cust (Robinia), elm, Soya, leaves of Begonia, bulb-scales of onion, 

 garlic, and leek, the root-stock of Iris, etc. 



(c) Cystoliths may be readily studied by making cross-sections of 

 the leaves of Urtica, mulljerry, hop, hemp, fisr, Celtis, and other Urti- 

 cncem. Tliey are said by Sachs to occur only in tliis order and the 

 Aeanthacem.* 



Fig. 48.— CyBtolith from the epidermis of the upper surface of the leaf of Urtica 

 fnacrophylla, from a cross section of the leaf. X 235. — After De Bary. 



(/) Plant-crystals appear to be surrounded by a thin layer of proto- 

 plasm ; probably they are separated out from the cell sap only through 

 the influence of protoplasm. It is further probable that they are resid- 

 ual products of chemical actions in the plant, and, as they appear never 

 to be made use of by the plant, we must regard them as to a certain 

 extent of the nature of excretions. 



*"Lehrbuch," 4te auf., p. 69. However, cystoliths, or structures 

 very much like them, may be found in the leaves of Ceanothus prostra- 

 ius of Nevada and California. The student is referred to De Bary's 

 " Vergleichende Anatomic der Vegetationsorgane der Phanerngamen 

 und Fame," Chapters I. and III., for a full discussion of the subject of 

 plant-crystals, and for a list of plants containing them. The articles 

 referred to in Qr. Jov/r. Mic. Science will also prove helpful. 



