222 TANNINS 



many are glucosides, and that oxidation readily takes place 

 with the ultimate formation of oxalic acid and carbon dioxide, 

 suggest that the substances under consideration may be reserve 

 food-material. 



Thus Schell, while acknowledging that tannin may some- 

 times 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 Echunn 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 accumu- 

 lated in bark and old leaves but would be translocated out of 

 such places before they were cast off, the same as are other mate- 

 rials in the generality of cases. But against this argument may 

 be cited the fact that fallen leaves may contain substances of un- 

 doubted 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 ; thus Warming has suggested that in 



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



