CRYSTALS. 55 



wood of Tectona grandis (Indian Teak).^ Holznei ' uses the 

 following reaction to detect calcic sulphate : a solution of baric 

 chloride (not too concentrated) is brought into contact with 

 the crystal under examination ; calcic sulphate soon becomes 

 covered with a whitish deposit of baric sulphate. This test 

 failed to show the presence of calcic sulphate in the plant- 

 crj-stals hitherto referred to this salt ; thej- all gave, however, 

 the reaction for the oxalate. 



188. Crystals closely resembling in most respects those which 

 are found in cells can be produced by Vesqne's method.'' Three 

 test-tubes are placed side bj' side : in the first is a moderately' 

 strong solution of calcic chloride ; in the middle one, a five per 

 cent solution of sugar; and in the third, a solution of potassic 

 oxalate. From the liquid in the first to that in the second a 

 short strip of filtering-paper runs, and a similar strip passes 

 from the second to the third test-tuhe ; and thus the liquids in 

 the three tubes are brought into indirect contact. Ciystals will 

 be formed in the middle tube, their character depending upon 

 the nature of the liquid there. In a solution of sugar, raphides 

 are produced ; in pure water, prisms of small size, but with 

 sharpl}- defined faces and angles. 



189. According to Souchay and Lenssen,^ monoclinic (" Clino- 

 rhombic ") crystals of calcic oxalate containing two equivalents 

 of water are produced upon quick precipitation, while bj' very- 

 slow action right octahedra with six equivalents of water are 

 formed. 



A few works of reference are the following : — 



MoHL. Principles of the Anatomy and Physiology of the Vegetable Cell. 

 Translated by Henfrey (London, 1852). An octavo of 158 pages. This is an 

 excellent translation of a classical work. 



HoFMEiSTEB. Die Lehre von der Pilanzenzelle (Leipzig, 1867). An octavo 

 of 397 pages. The volume treats very fully of the physical properties of pro- 

 toplasm. 



Ebermayek. Physiologische Chemie der Pflanzen (Berlin, 1882). This is 

 the first volume of an expensive work which deals with the relations of plants 

 to soil and climate. 



HusEMANN und HiLGEK. Die Pflanzenstoffe (Berlin, 1882). Two large 

 volumes. It has very extensive references to the literature of the subject, and 

 most of its abstracts are excellent. 



1 Pies : Faturkundig Tijdschrift voor Nedrlandsch-Indie, 1858, p. 345. 

 Quoted from Holzner. 



^ Flora, 1864, p. 283. This communication contains a good abstract of the 

 literature of plant-crystals up to 1862. 



' Ann. des Sc. nat, ser. 5, tome xix., 1874, p. 300. 



* Annalen der Chemie und Phai-macie, c, 1856, p. 311. 



