PHYSIOLOGY 217 



quired after the tannin has disappeared it is not impossible 

 that the latter may have some connexion with the formation 

 of fruit esters. 



Other suggestions regarding the value of tannin are not 

 wanting ; thus Moore * states that it may play an important 

 part in the lignification of cell walls. 



More recently Drabble and Nierenstein f have come to 

 the conclusion that tannins play an important part in cork 

 formation, and are acted upon in the plant by formaldehyde 

 and acids and are precipitated in the walls of the cork cells. 

 Reasons for this theory may be alluded to briefly. 



There occur in plant tissues tannins ; phenols such as 

 phloroglucinol, resorcinol and hydroquinone ; and hydroxy- 

 benzoic acids, such as gallic, salicylic, and protocatechuic acids. 



When these substances are treated with hydrochloric acid 

 and formaldehyde various condensation products are precipi- 

 tated. These condensation products can be produced from 

 gallic acid, pyrogallol, protocatechuic acid, phloroglucinol, 

 salicin, tannic acid, and other substances, simply by passing a 

 slow stream of carbon dioxide through the mixture of formal- 

 dehyde and the tannic acid, for example. 



The reactions given by these bodies are similar to those 

 characteristic of cork ; thus they are insoluble in Schweitzer's 

 reagent and strong sulphuric acid, but readily dissolve in strong 

 potash. It is, therefore, possible that in cork formation simi- 

 lar condensation products may play a part, for the requisite 

 materials are present in the plant. 



Further, in the plants examined, the presence of gallic or 

 tannic acids was indicated in the immediate neighbourhood 

 where cork was being formed, and by suitable means there 

 can be obtained from cork, products having the same mother 

 substance as the condensation products mentioned above. 



Still more recently Van Wisselingh has published certain 

 observations from which he concludes that tannin plays an 

 important part in the formation of cell walls in certain cases, 

 for instance Spirogyra. He does not consider it a reserve food- 

 material as such, but rather a soluble substance which the 



* Moore: loc. cit. 



t Drabble and Nierenstein: " Biochem. Journ.," igo6, 2, 96. 



