5 8 BOTANICAL MICROTECHNIQUE. 



in Fig. 21. Here Fig. I shows a tetragonal pyramid, Figs. 

 II and III combinations of pyramid and prism, Fig. IV 

 a monosymmetric rhombohedron, Fig. V a rhombic plate, 

 Fig. VI probably a combination of positive and negative 

 hemipyramids with the basal plane, Fig. VII a combination 

 of the rhombic plate (Fig. V) with the clinopinacoid, Fig. 



FIG. 2i. Crystals of calcium oxalate. I-III, from the spongy parenchyma of Tra_ 

 descantia discolor ; IV, from Cycas circinalis ; V, Musti paradisieica ; VI, Citrus vul- 

 garis; VII and IX, Guaiacum officinnle ; VIII, Citrus medica, IV, V, VII, IX after 

 Holzner ; VI after Pfitzner. 



VIII a combination of the rhombohedron (Fig. IV) with 

 a hemipyramid, Fig. IX a twin crystal whose angle xyz 

 measures 141 3', according to Holzner (I, 34). Calcium 

 oxalate is also especially common iii the form of fine 

 needles (" raphides ") or tiny slivers (" crystal sand ") on 

 which no crystallographically determinable faces or angles 

 can be recognized ; and sphaerocrystals have been seen 

 (cf. Kohl's compilation, II, 15). 



Calcium oxalate is insoluble in water and acetic acid ; but 

 in hydrochloric acid it is soluble, though the solution of the 

 larger crystals, especially if they are imbedded in mucilage, 

 does not occur at once. It is best to place the preparations 



