54 THE VEGETABLE CELL IN GENERAL. 



crystals for examination, tlieir chemical composition has not jet 

 been determined with certainty in all cases. Tliat a protoplas- 

 mic film usually envelops both solitary and aggregated crystals, 

 can be shown by the method pointed out hj Pa3-en ; ' namely, 

 1)3' dissolving tlie crystal slowly in very dilute nitric acid, and 

 testing with iodine, when the film will become yellowish-brown. 

 It has also been made out be3ond question that some crystals 

 have a considerable admixture of cellulosic matter, and that a 

 few others are covered by a membrane of cellulose.'' But these 

 two substances do not obscure the chemical reactions in ordinary- 

 cases, by which it has been shown that the larger number of crys- 

 tals consist of calcic oxalate, after which, in frequency of occur- 

 rence, comes the carbonate of the same metal. These two salts 

 can be easily distinguished from each other by the following 

 simple tests : — 



Since those two salts may occur in the same specimen, it is best 

 to use acetic acid first ; by this agent all traces of the carbonate 

 are removed, and hydrochloric acid can then be applied in order 

 to detect the presence of oxalates. Sanio ' and Holzner have 

 shown conclusively that many crystals which have been supposed 

 to be calcic carbonate consist merely' of the oxalate. 



Crystals of calcic sulphate have been repoi'ted as occurring 

 in certain Musacea?,' in the bark of the willow, in the roots of 

 aconite, bryony', and rhubarb ; and also in the root of a 3'oung 

 bean.^ Calcic phosphate is said to have been detected in the 



1 Payen : Mem. des savants Strangers, ix., 1846, p. 91. 



2 Eosanoff (Bot. Zeit., 1865, 1867), Crystals in pith of Ricinus and Kerria. 

 Pfitzer (Flora, 1872), crystals in the leaves of orange and the bark of many 

 trees. 



Hilgers has investigated the occurrence of crystals at different periods of 

 growth of different oi-gans. From his results it appears, (1) that in the veiy 

 youngest parts no crystals are to be found ; (2) they appear, however, very 

 early in most parts, and (3) speedily attain their maximum size, after which 

 they undergo no change (Pringsheim's Jahrb., vi., 1867, p. 285). 



s Sanio : Monatsber. Berliner Akad., 1857. 



* Van Tieghem ; Traite de Botaniqup, p. 526. 



* Sitzungsberichte der Wiener Akad., xxxvii., 1859, p. 106. 



