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 (Si02) occurs in a number of plants either as 
an incrustation in the cell wall as in Diatoms, 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. 
18. 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. 
