276 TANNINS 



Schell, while acknowledging that tannin may sometimes 

 be a bye-product of metabolism, considered that at other 

 times it might be used up in the construction of higher com- 

 pounds which would serve as food. He found that, in the 

 germination of the oil-containing seeds of Echium vulgare and 

 other Boraginaceae, as the oil is used up the tannin begins 

 to play a part in the constructive metabolism and gradually 

 diminishes in amount. Further, if such seeds be germinated 

 in the light the tannin increases in quantity. For these and 

 other reasons he concluded that such a use of tannin only ob- 

 tained when there was a scarcity of the more normal foods 

 such as starch and oil. 



A consideration, however, of other facts does not tend to 

 support the idea of tannin being of the nature of a reserve 

 food. Hillhouse,* for example, found that if a fuchsia having 

 an abundant supply of tannin be grown in the dark, there is 

 no diminution in the substance in question. Then again the 

 facts of its distribution are against this particular view ; for 

 example, it does not occur in sieve tubes which transport both 

 sugar and other food substances ; there is, in many cases, not 

 a great discrepancy in the tannin-content of fully mature and 

 fallen leaves, for naturally it would be expected that if tannin 

 were of any considerable value as a food-stuff it would not be 

 accumulated in bark and old leaves but would be translocated 

 out of such places before they were cast off, the same as are 

 other materials in the generality of cases. But against this 

 argument may be cited the fact that fallen leaves may contain 

 substances of undoubted value to the plant, such as nitrogen 

 and phosphorus, and even glucose and starch. In evergreen 

 leaves there is no diminution in the quantity of tannin during 

 the winter months, which may mean that either it is of no 

 great value or that, since growth is more or less at a standstill, 

 the plant has more food than it requires immediately, or that 

 it subserves some biological function. 



On the other hand, the figures obtained by Levi and 

 Wilmer, mentioned above, require some explanation ; why 

 should a minimum of tannin occur in the leaves in June 

 * Hillhouse : " Midland Naturalist." 1887-8. 



