PHYSIOLOGY 223 



this particular connexion the tannin may 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 

 amount of tannin, more especially in germinating seeds, Van 

 Wisselingh points out that the amount found at any particular 

 moment represents the balance as it were of the tannin ac- 

 count ; that is to say, if more tannin is formed than is decom- 

 posed, an increase in the tannin content will result and vice 

 versa, so that in one and the same plant there will be some- 

 times an increase and sometimes a decrease according to the 

 conditions obtaining. It does not necessarily follow, and this 

 is applicable to many things besides tannin, that because there 

 is an increase in the amount, therefore the substance is of no 

 value in constructive metabolism. 



Tannin has been considered an important constituent of 

 the osmotic substances of the cell ; although this may be true 

 for some tannins it probably does not hold for all, since no 

 ill effects follow the precipitation of tannins in the living cell 

 by means of methylene blue ; also, in certain cases, it is not 

 renewed when precipitated. 



A biological significance is not infrequently attached to 

 tannins ; thus it may be of use against animals, it may be 

 connected with the activity of nectaries in providing sugar, 

 and it has been suggested by Moore that when it occurs in 

 the epidermis of leaves, it may play a part in the opening and 

 closing of stomata. 



Finally, it may be of considerable value as an antiseptic, 

 preventing the germination and growth of parasitic Fungi. In 



