88 PHARMACEUTICAL BOTANY 



lar spheroidal or ellipsoidal deposit. These structures are abun- 

 dantly found in the plants of the Nettle Family and constitute a 

 leading peculiarity of the same (see Fig. 87). 



Hair cystoliths differ from the average type in that they are 

 devoid of a stalk. Such are seen in the non-glandular hairs of 

 Cannabis sativa. 



The calcium carbonate incrustation of a cystolith dissolves with 

 effervescence on the addition of a mineral or organic acid. 



17. Silica. Silica (SiO 2 ) occurs in a number of plants either as 

 an incrustation in the cell wall as in Diatoms v the Equisetinea and 

 Graminea or more rarely in the form "silica bodies" such as are 

 found in certain Palms, Orchids and Tristicha. It is insoluble in 

 all the acids except hydroflouric. It may be obtained in pure form 

 by placing tissue containing it in a drop or two of concentrated 

 sulphuric acid and after a time treating with successively stronger 

 solutions of chromic acid (starting with 25 per cent.) and then wash- 

 ing with water and alcohol. 



1 8. Tannins. Tannins are amorphous substances occurring in 

 plants having an astringent taste, and turning dark blue or green 

 with iron salts. They occur in greatest quantity in the bark of 

 exogens, and in gall formations. They are soluble in water, alcohol 

 glycerine, and a mixture of alcohol and ether. They are almost 

 insoluble in absolute ether and chloroform. They give insoluble 

 precipitates with organic bases such as alkaloids and with most of 

 the salts of the heavy metals. 



According to their behavior with solution of iron chloride or 

 other soluble iron salts two kinds of tannic acid are recognized: (a) 

 a form of tannic acid giving a blue color, as that which is found in 

 Rhus, Castanea, Granatum, Galla, etc.; (b) another tannic acid 

 producing a green coloration, as that found in Krameria, Kino, 

 Mangrove bark, Quercus, Catechu, etc. 



If sections are placed in a 7 per cent, solution of copper acetate 

 for a week or more, then placed on a slide in 0.5 per cent, aqueous 

 solution of ferric chloride, and after a while washed with water and 

 mounted in glycerin, an insoluble brownish precipitate will be pro- 

 duced in those cells containing tannin. 



