THE METABOLISM OF PLANTS. 249 



The waste-products are usually deposited in the cells in which they 

 are produced, or in intercellular spaces (e.g. resin passages) : there are 

 thus two kinds of receptacles for excretions, cellular and intercellular. 

 Some of them (calcium carbonate and oxalate, alkaloids) are especially 

 deposited in parts of the plant which are deciduous, such as leaves, fruits, 

 seeds, and bark. Calcium carbonate and oxalate are deposited usually in 

 the form of crystals either in the cell-wall or in the cell-cavity, and silica 

 in the cell-wall. Allusion has already been made (p. 22) to the presence 

 of these substances in the cell-wall, especially to the deposition of calcium 

 carbonate in crystoliths (Fig. 34) ; these bodies are apparently peculiar 



Fig. 34 (after de Bary). Cystolith from the leaf of Urtica macrophylla. 



to the orders Urticaceae, Euphorbiaceae, and Acanthaceae. Molisch 

 has observed that calcium carbonate is commonly to be found in the 

 cells and vessels of the heart-wood (duramen) of dicotyledonous trees. 

 Calcium oxalate is deposited in cells as either single crystals or a cluster 

 of crystals belonging to the quadratic system (CaC 2 O 4 -l-2H 2 O), or in 

 groups of parallel prismatic crystals (raphides), resembling a bundle of 

 needles, belonging to the clinorhombic system (CaC 2 O 4 + 6H 2 O). Some- 

 times the crystals, belonging to either system, are arranged in a radiate 

 manner so as to form a sphere-crystal, as in the hyphae of Phallus 

 caninus, a Basidiomycetous Fungus. 



BIBLIOGRAPHY. 



Hoppe-Seyler ; Zeitschr, f. physiol. Chem., Ill, 1879. 



Sachs; Bot. Zeitg. 1862; Flora, 1863. 



Cunningham; Q. J. M. S, XX, 1880. 



Naegeli ; Sitzber. d. k. Akad. in Miinchen, 1879. 



von Rechenberg; Journ. f. prakt. Chem., 1881, and Deut. Chem. 



Ber., 1 88 1. 

 Hoppe-Seyler; Physiol. Chem. I, 1877: also Schulze and Barbieri 



Journ. f. prakt. Chem., 1882. 

 Schiitzenberger; Comptes rendus, LXXVIII, 1874. 

 Salomon; Verhandl. d. physiol. Ges. zu Berlin, 1880. 

 Reinke and Rodewald; Unters. a. d. bot. Lab. in Gottingen, II, 1881. 



