8 THE ROYAL SOCIETY OF CANADA 



oxidized tannin and the coagulated emulsoid, and not, as recently 

 asserted by de Dominicis (1919) on the authority of Gerber, to the 

 oxidation of the tannin, as I have previously shown (I.e.)- 



The change in adsorption equiHbrium, as would be expected, is related to the 

 degree of swelling. This, in turn, depends upon the concentration of the acid or 

 base present, as shown by the following experiment. Tannin masses taken from 

 a very ripe fruit,^ four days after the first wateriness had appeared, were placed in 

 hydrochloric, sulphuric and nitric acids, each in the concentrations N/1000, N/100 

 and N/10, with water as control. The accompanying photograph (PI. 3) shows the 

 variety of response at the end of three days. Since the presence of organic acid 

 may prevent the precipitation of the emulsoids by tannin, as in the case of tannin- 

 albumin, we may interpret the appearances presented in the photograph by con- 

 cluding that the greatest diffusion of tannin occurred in the highest concentration 

 in which, as a matter of fact, the greatest amount of swelling occurred. It will be 

 observed, however, that in the control there seems to be a much larger amount of 

 diffusedly precipitated tannin. It may be that the apparently less precipitation 

 in the concentrations N/1000 and N/100 is due not to the less escape of tannin, but 

 to the inhibiting effect of the small amount of acid on the formation of tannin 

 precipitation membranes; while at the higher concentration of acid, a coagulation of 

 substances, capable of adsorbing tannin after coagulation, has taken place. How- 

 ever this may be, it is, I think, quite certain that the experiment definitely proves 

 that the adsorption equilibrium is affected by the degree of swelling of the intra- 

 cellular emulsoid. 



The behaviour above described, variants of which have been 

 observed, not only in the moribund cells which occur in tissues de- 

 stined to die, such as those in fruit pericarps, but also in cells which 

 take sustained part in the activity of the plant body (cotyledons, 

 leaves, etc.), coupled with the supposed toxicity of tannin, has em- 

 boldened me to advance the theory that the protoplast, when tannin 

 occurs, is in general protected from its toxic effect by its adsorption 

 by another body. Were tannin a by-product only, and known to be 

 toxic, of which, as a general statement, there is doubt, the theory 

 would have much to recommend it. But at present the evidence is 

 too contradictory to permit its acceptance in more than a usefully 

 tentative way. 



In the first place, a critical observer such as van Wisselingh 

 denies the presence of an adsorbing body. His studies of Spirogyra 

 maxima (1910, 1914) persuaded him that Wigand in 1862 had come 

 to the correct conclusion, namely, that tannin is an essential factor 

 in plant metabolism and that physiologically it is a link in the carbo- 

 hydrate chain of events leading to the building up of the cell wall. 



V'an Wisselingh's experiments in Spirogyra would deserve more 

 than mere mention, if time and space permitted. The results are in 



^Persimmon of the variety "Zengi." 



