It seems to be fairly well demonstrated that tannins are intermediate products for the formation of cork tissue. This may account for their common occurrence in the wood and bark of trees. Indeed, it has been shown that gallic and tannic acids are present in considerable proportions in those parts of the plant where cork is being formed. Further, that they bear direct relation to cork-formation has been demonstrated in two different ways. First, cork-like substances have been artificially produced by passing a stream of carbon dioxide through mixtures of formaldehyde with various tannic acids. Second, by various treatments of cork, decomposition compounds showing tannin-like properties may be obtained. Some investigators have held that not only cork tissue but also other lignose, or cell-wall material, may be developed from tannins. Certain observations with _Spirogyra_ seem to indicate that tannin may play an important part in the formation of new cell walls during conjugation, as cells which are ready to conjugate are rich in tannin, which gradually diminishes in quantity until it is practically absent at the time of spore-formation. There seems to be no evidence that tannins perform any such function as this in higher plants, however. Again, tannins may play a very important part in pigment-formation. They are very similar in structure to the anthocyanin pigments, both being made up of practically identical decomposition units, the phenolic bodies. The disappearance of tannins during the process of ripening of fruits may be connected, in part at least, with the development of the brilliant red, blue, and yellow pigments which give such rich colors to the thoroughly ripe fruits. Finally, certain of the tannins undoubtedly serve as protective agents to prevent the growth of parasitic fungi in fruits, etc. Recent investigations show that at least some of the varieties of fruits which are resistant to the attacks of certain parasitic diseases utilize tannins for this purpose. This protective effect may be accomplished in two different ways. Either the tannin actually serves as an antiseptic to prevent the growth of the parasitic fungus within the tissues of the host plant, or it assists in the development of a corky layer which "walls-off" the infected area and so prevents further spread of the disease through the tissue. Examples of both types of protective action have recently been reported. It is obvious that the different forms of tannins may play different rôles in plant life, and the same tannin substance may possibly serve different purposes under different conditions. BIOLOGICAL SIGNIFICANCE OF TANNINS IN FRUITS The presence of tannins in fruits and the changes which they undergo during the ripening process cannot fail to attract attention to their biological significance in serving to protect the fruit from premature consumption as food by animals.