MICR CHE MIS TR Y. 63 



Marattiacea hexagonal plates, which, according to the reac- 

 tions carried out by him, must consist of gypsum with an 

 admixture of magnesium sulphate. The correctness of these 

 views has, however, been disputed by Monteverde (II), 

 according to whom the crystals in question consist merely 

 of calcium oxalate. Gypsum occurs abundantly, however, 

 -according to Monteverde, dissolved in the cell-sap, and is 

 deposited in the form of sphaerocrystals after lying for 

 months in alcohol. In the same way, a deposit of sphaero- 

 crystals consisting of gypsum is produced in Hebeclinium 

 macrophyllum by alcohol, especially in the young wood-cells, 

 according to Hansen (I, 118). 



d. Calcium Tartrate, CaC a H 2 .(OH) a .(COO) a . 



95. In the yellowed leaves and petioles of Vitis and 

 Ampelopsis, Schimper (II, 238) found rhombic crystals of 

 calcium tartrate, which sometimes reach considerable size, 

 especially in the parenchyma of the bark and pith of the 

 petiole of Vitis Labrusca. They represent largely a combi- 

 nation of the prism and dome, but the most various fusions 

 also occur (cf. Fig. 23). These crystals 

 are very slightly soluble in water, but 

 very easily soluble in caustic potash solu- 

 tion, almost instantly so in a \<yf> solution, 

 which does not attack calcium oxalate. FlG 23 ._c a icium tar- 

 Their behavior with acetic acid is also 



characteristic. Calcium tartrate crystals R 

 are easily soluble in dilute solutions con- 

 taining about 2% of glacial acetic acid, while in the piire 

 glacial acid, or even in a 50$ solution of it, they are insoluble. 

 In consequence of this, it may be observed, in sections to 

 which concentrated acetic acid has been very gradually 

 applied, that a recrystallization of previously dissolved crys- 

 tals occurs. 



Calcium tartrate crystals are doubly refractive, but this 

 power seems to me much less than that of the monoclinic 

 crystals of calcium oxalate. On burning they are converted 



