PHYSIOLOGY 219 



Various facts on the relation between tannin and other 

 substances such as starch, sugar, resin, etc., have led to 

 various opinions. 



That starch frequently is contained in the same cells with 

 tannin suggests a connexion between the two, and it is not 

 impossible that the starch may contribute the glucose for the 

 construction of the tannin. In the case of Pinus, it has 

 already been mentioned that in the spring, when the flow of 

 resin is most copious, the tannin decreases as the resin in- 

 creases; also the cells surrounding the epithelium of resin 

 ducts contain tannin and starch. Wiesner, therefore, con- 

 cluded that tannin is an intermediate product in resin forma- 

 tion. 



Tannin is not uncommon in unripe fruits, and the amount 

 of these astringent substances diminishes during ripening. 



According to Bassett* "the amount of tannin in fruits 

 varies with certain factors, such as injury, length of time be- 

 tween removal from tree and analysis, etc. The presence and 

 relative amount of this tannin or tannin-like body is con- 

 trolled by the presence of certain enzymes which vary in 

 amount and activity during the growth of these fruits." 



Buignet, from the fact of the diminution of tannin and 

 starch which occurs concurrently with the increase in sugar, 

 considered that the sugar in the ripe fruit (e.g. Musa) is 

 formed from these two substances. This opinion, however, is 

 not held by Gerber who investigated the same phenomenon. 

 In Diospyros Kaki he found the young fruit to be very 

 astringent, but not so the ripe fruit He considers that the 

 tannins disappear by complete oxidation without the forma- 

 tion of carbohydrates. One reason for his opinion is that in 

 the conversion of tannin into carbohydrate more carbon diox- 

 ide would have to be liberated than oxygen absorbed, where- 

 as in fruits the relation is the reverse. 



On the other hand, he does consider the tannins to be of 

 some value, for they, by the formation of pectins, may limit 

 the loss of carbohydrate. 



Further, inasmuch as the pleasing odours of fruit are ac- 



* Quoted from the footnote appended to a paper on the Toxicity of Tannin 

 by Cook and Taubenhaus: "Delaware Coll. Agric. Exp. Station" Bull., 91, 

 1911. 



