PHYSIOLOGY 277 



when photosynthesis is so very active ? Is it used up in the 

 construction of other substances or is it merely translocated 

 to other parts such as the bark ? If the latter be true, the 

 further question arises, then why should it be transferred at 

 one time of the year and not at another ? 



Of course, it is possible that these and like variations may 

 be explained by the varying conditions of, say, light, tempera- 

 ture and moisture ; and with regard to this variation in the 

 amount of tannin, more especially in germinating seeds, van 

 Wissehngh points out that the amount found at any particular 

 moment represents the balance as it were of the tannin 

 account ; that is to say, if more tannin is formed than is de- 

 composed, an increase in the tannin-content will result and 

 vice versa, so that in one and the same plant there will be 

 sometimes an increase and sometimes a decrease according to 

 the conditions obtaining. It does not necessarily follow, and 

 this is applicable to many things besides tannin, that because 

 there is an increase in the amount, therefore the substance is 

 of no value in constructive metabolism. 



A biological significance is not infrequently attached to 

 tannins ; thus it may be of use against animals, it may be 

 connected with the activity of nectaries in providing sugar, 

 and it has been suggested by Moore that when it occurs in 

 the epidermis of leaves, it may play a part in the opening and 

 closing of stomata. 



Finally, it may be of considerable value as an antiseptic, 

 preventing the germination and growth of parasitic Fungi. In 

 this connection Cook and Taubenhaus * have found that in 

 many cases tannin has a tendency to retard or inhibit the 

 growth of Fungi, the parasitic forms being more sensitive than 

 the saprophytic. In some cases the spores are killed, whilst 

 in others germination is much impeded. On the other hand, 

 low percentages of tannin may in some instances stimulate 

 germination and also fruiting. The behaviour of Fungi 

 towards tannin varies with the species and sometimes even 

 with the individual, more especially in the case of spores. 

 ^ To conclude, the different substances included under the 



* Cook and Taubenhaus : " Delaware Coll. Agric. Exper. Station," 

 Bull. 91, 1911. 



