ALLIED AND MISCELLANEOUS PRODUCTS 189 



found, but in the bark and leaves which are cast off. Furthermore, 

 plants rich in tannins, according to Hillhouse (1888), do not draw 

 upon their tannin reserves when grown in the dark as would be 

 expected. In evergreen leaves there is no diminution during the 

 winter when other foods are not being manufactured, although 

 this might be explained by the fact that other reserves are used 

 first. Schell found that the tannin in oily seeds was used only 

 when the oil reserves were gone. 



2. The tannins are more likely waste products than reserve 

 foods. The distribution in the leaves and bark agrees with this 

 hypothesis. In rapidly growing leaves and shoots, in growing 

 points, in germinating seeds, and in very irritable regions like 

 pulvini, where the protoplasm is especially active, tannins are 

 found. They are not intermediate products in the formation of 

 proteins but, according to Sachs, are waste products resulting 

 from their decomposition. The glucose is attached to the com- 

 pound in order to make it more soluble and to facilitate its trans- 

 port. 



3. In the pines, the resin is more abundant in the spring, and 

 the tannins decrease as the resin increases. The cells around the 

 resin canals are also rich in tannin and starch. For these reasons, 

 Wiesner concluded that tannins were an intermediate product in 

 resin formation. 



4. Tannins are present in unripe fruits, imparting to them their 

 characteristic astringent taste familiar in green apples and green 

 persimmons. This generally disappears as the fruit ripens, while 

 sugars, the fruit esters which give the specific aromas, and the 

 bright-colored pigments, develop. Some investigators have thought 

 that the tannins give rise to the sugars, esters, and pigments. There 

 is good evidence to support the relation between the fruit pigments 

 and the tannins, and even some of the sugars and esters may arise 

 in this manner; but it has recently been shown that the tannins 

 do not actually disappear in ripe fruits. Instead they are inclosed 

 in special cells surrounded by an insoluble membrane and, as a 

 result, when they are eaten by an animal there is no disagreeable 

 taste. This membrane formation may be hastened by various 

 chemical agents, among which is carbon dioxide gas; and the 

 artificial ripening of persimmons by this method is now a standard 

 commercial process. The walling off of the tannins as the fruit 

 ripens is an important biological factor in fruit distribution, and 



