10 THE ROYAL SOCIETY OF CANADA 



Dominicis, 1919) or at even higher concentrations (for which Dekker, 

 1913, gives full statistics). But I am inclined to think that when this 

 is the case the containing cells are to be found in tissues which are 

 on the road to necrosis. In such cells the tannin accumulates toward 

 a maximum and probably does not again enter as a factor in the 

 metabolism of the plant. It may be true that tannin in some plant 

 products may have a discouraging, not to say a depressing, effect on 

 marauding rats or snails or such like cattle; but with teleological 

 interpretations I am not here concerned. 



It must not be lightly overlooked that other substances than an 

 emulsoid may, by some form of antagonism, produce the effect of 

 preventing the protoplasm from adsorbing the tannin, should it be 

 shown that the latter is toxic. It is evident, e.g., that sugars may 

 bear some such relation (Hillhouse, 1887, p. 22; Knudson I.e.). The 

 theory which I have advanced is applicable no matter what substance 

 may be found to have the power of binding tannin sufficiently to 

 inhibit its attack upon protoplasm. Here we must also point out 

 that toxicity and metabolic usefulness are not mutually exclusive. 

 Tannin, though toxic, may still be one of the links in the carbohydrate 

 chain, of which cellulose may be the last. If it should eventuate that 

 this is true, we should be the more compelled to seek an explanation 

 for the apparent indifference of protoplasm toward its toxicity. 



In general support of the view that tannin is useful we should 

 note that it is, in some cases, believed to be dependent upon light for 

 its formation in leaves (see Dekker I.e.); that it disappears in the 

 case of Spirogyra when kept from the light (van Wisselingh I.e.) and 

 that it can be used as a nutrient (Knudson) by some organisms. 

 That it furnishes little energy is of minor importance if its rôle be a 

 necessary step in a progress of events. But I now find myself entering 

 upon a more general phase of the discussion, in pursuing which I 

 would only be repeating what has been very well summarized already 

 by Dekker, van Wisselingh, and, earlier, by W. Hillhouse, a perusal 

 of whose presidential address to the Mason College Botanical Society 

 in 1887 reminds us that during the years intervening between them 

 and now we have not gone very far in the solution of the tannin 

 problem. We may take, however, a further moment to see what 

 now may be said in answer to the questions put at the beginning of 

 this paper. 



To the first question we may answer that it is certainly known 

 that in many cases the tannin in the vacuole is engaged in adsorption 

 equilibrium by a second body, which has been identified for certain 

 of these cases as a cellulose-like body. That albumin is an adsorbing 



