PHYSIOLOGY 221 



tained when there was a scarcity of the more normal foods 

 such a. 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 

 this particular connexion the tannin ma*y be of value in 

 protecting the plant against undue evaporation during the 

 winter, and further it may be a means of rapidly restoring lost 

 turgor. 



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 

 when photosynthesis is so very active? is it used up in the 

 construction of other substances or is it merely translocated to 

 other parts such as the bark? If the latter be true, the 

 further question arises, then why should it be transferred at 

 one time of the year and not at another ? 



Of course, it is possible that these and like variations may 

 be explained by the varying conditions of, say, light, tempera- 

 ture and moisture; and with regard to this variation in the 



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



