PHYSIOLOGY 217 



considerably decreases in darkness owing to translocation and 

 other processes. 



This, however, is not the only origin for tannin, for if 

 tannin-containing seeds, e.g. the oak, be germinated in dark- 

 ness, there is an increase in the amount of tannin ; further, the 

 production of various aromatic compounds may be a stage in 

 the synthesis of proteins, and some of these may eventually 

 give rise to tannin. 



The facts regarding the distribution of tannin have an im- 

 portant bearing on the subject. It is abundant in leaves ; in 

 parts in which growth is very active, such as growing points ; 

 in galls and other pathological growths ; also it is found in 

 association with secretory organs, such as gland cells of Sar- 

 racenia and Utricularia, and in parts in which the protoplasm 

 is especially irritable, such as pulvini. Pfeffer found that in 

 young fully formed pulvini no tannin occurs, but it appears 

 soon after movements commence and gradually increases in 

 quantity until the leaf dies. 



In the case of Robinia pseudacacia the pulvini of the leaf- 

 lets contain less tannin than the main pulvinus, which is much 

 less sensitive than are the secondary pulvini. 



The consideration of these facts supports the conclusion 

 arrived at by Sachs that tannin results from intense meta- 

 bolism such as occurs in active leaves ; in rapid tissue forma- 

 tion, as in galls and vegetative apices ; during germination 

 and secretion ; and as a consequence of particular stimulation, 

 as in mobile pulvini. 



Various facts on the relation between tannin and other 

 substances such as starch, sugar, resin, etc., have led to 

 various opinions. 



That starch frequently is contained in the same cells with 

 tannin suggests a connexion between the two, and it is not 

 impossible that the starch may contribute the glucose for the 

 construction of the tannin. In the case of Pinus, it has 

 already been mentioned that in the spring, when the flow of 

 resin is most copious, the tannin decreases as the resin in- 

 creases; also the cells surrounding the epitheliufri of resin 

 ducts contain tannin and starch. Wiesner, therefore, con- 

 cluded that tannin is an intermediate product in resin forma- 

 tion. 



