268 TANNINS 



in the bark, oiQuercus, many species of Ccesalpinia, Eucalyptus 

 occidentalis, Castanea, and Humulus ; in the leaves of Cerasus, 

 Rhus, Ficus, and Rhododendron ; in the fruit, especially if un- 

 ripe, of Terminalia Chebula, CcBsalpinia coriaria, Pyrus, and 

 Phaseolus ; and more rarely in the seeds, either before or 

 after germination, of Areca Catechu, Echium vulgare, and other 

 Boraginaceae. 



Further, tannin is often found in more or less special 

 structures, e.g. the cells of the pulvini of Mimosa pudica 

 and Rohinia pseudacacia ; in the gland cells of Sarracenia and 

 Utricularia ; in the hairs of Primula and Hedera ; and also 

 in laticiferous tissue.* 



Finally, it may be remarked that it is especially abundant 

 in pathological growths such as galls, which may contain from 

 25 to 75 per cent of tannin. 



Kraemer f has investigated the galls formed by the agency 

 of Cynips aciculata, a gall fly, upon Quercus coccinea. He found 

 that during the chrysalis stage gallic acid was produced, prob- 

 ably at the expense of the starch, and as the imago developed 

 the gallic acid gave place to tannic acid. 



Tannin occurs in solution in the cell sap and sometimes in 

 distinct vacuoles. According to Lloyd, J in the former case 

 the tannin is linked up or adsorbed with other cell constituents 

 which, in some instances, is a cellulose-like body. Similarly 

 Herszlik § on microchemical evidence concludes that the tannin 

 vacuoles in the cortical cells of Phaseolus are surrounded by 

 a membrane of a pectic nature. Probably this, or a like, 

 protective arrangement is general for otherwise the protoplasm 

 would be precipitated by the tannin. 



The amount of tannin present in certain plants varies 

 according to the physiological state, the season of the year, and 

 the conditions of growth. 



In Pinus it is stated that the amount of tannin varies 

 with that of the resin ; thus in the spring it was found that as 



* For details of the distribution of tannin in Ribes, etc., see Dekker : 

 " Rec. trav. bot. neerlandais," 1917, 14, i. 

 t Kraemer : " Bot. Gaz.," 1900, 30, 274. 

 X I-loyd : " Trans. Roy. Soc. Canada," 1922, i6, i. 

 § Herszlik : " Bull. Acad, polonaise," 1925, 3, 315. 



