136 PLANT ANATOMY. 
inclosed starch or had originated therefrom, as indeed both 
appear in the same tissues simultaneously, or still more often 
alternately. Nevertheless, tannin does not exist to any consid- 
erable amount in seeds. The amount of tannin contained in 
certain organs, such as barks and fruits, is subject to considera- 
ble periodical fluctuations.* : 
Tannin which is deposited in the purest form dissolves when 
subjected to examination under water. In order to bring it to 
view, the sections must therefore be observed under benzol, 
volatile or fatty oils, or other liquids which do not dissolve the 
tannic matter; even glycerin suffices, since it dissolves but little 
tannin when concentrated. Thus in galls, shapeless masses are 
found which almost completely fill the cells.?. The tannic mat- 
ter also very frequently penetrates the cell-membranes, so that 
the walls of entire tissues become colored after being moistened 
with a solution of iron, thus, for instance, the parenchyma of 
the Cinchona barks, the fibro-vascular bundles and the surround- 
ings of the oil-cells in cloves, ete. Thick, hard cell-walls, which 
do not become thoroughly moistened by an aqueous solution of 
iron, often assume, nevertheless, the blue or green coloration 
upon the simultaneous addition of alcohol. These reactions, 
however, are perhaps more often produced by derivatives, decom- 
position products of the tannins, or bodies otherwise related to 
them, such as ellagic acid or gallic acid, the presence of which 
in nature can, moreover, not yet be accepted with complete cer- 
tainty. Morin and morin-tannic acid, which react in the same 
manner with iron salts, have also not yet been met with in those 
parts of plants to which we here devote attention. Further- 
more, pyrocatechin, quercitrin, and rutin must not be omitted 
here, which likewise color solutions of ferric salts green. The 
_ first-mentioned substance can, indeed, be cited here only asa 
very subordinate constituent of kino, and quercitrin is contained 
‘Compare Wiegand, “ Satze iiber die physiologische Bedeutung des 
Gerbestoffes und der Pflanzenfarben.” Botanische Zeitung, 1862, 121; 
and Kutscher, ‘* Ueber die Verwendung der Gerbsdure im Stoffwechsel 
der Pflanze.” Flora, 1883, _ 
* Berg’s ‘‘ Atlas,” Plate 49, Fig. 136. 
