PHYSIOLOGY 219 



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 

 plant makes use of in elaborating other materials. This con- 

 clusion is in ^reement with the opinions held by Wingand 

 and published in 1 862. Van Wisselingh worked with Spirogyra, 

 and the main facts on which he based his conclusions are as 

 follows. Cells which are about to conjugate are rich in tannin, 

 and as the process of conjugation proceeds, there is a gradual 

 diminution in the amount of this substance, so that the mature 

 zygospore contains nothing more than mere traces. 



If conjugation be interrupted at an early stage, there is 

 still an increase of tannin, so that when death results there is 

 relatively a large quantity present. This accumulation may 

 be used as an argument in support of the view that tannin is 

 a waste product. Van Wisselingh, however, remarks that this 

 should not be a source of wonder, for in this case " It is not 



