S92 Mr Gardiner, On the general occurrence [May 28, 



Tannin occurs very widely distributed in every part of the 

 plant. Usually met with in isolated cells, it may be present in 

 canals or passages, e.g. Angiopteris, Acorus. It is also found in 

 laticiferous cells and vessels. It is produced abundantly in 

 leaves, e.g. Cerasus, Rhododendron, Ficus, &c; in stems, e.g. Hu- 

 mulus, Pinus, &c. ; in roots, e g. Kramerea, Aspidium, and is stored 

 up in large quantities in the bark, e.g. Quercus. Besides this it is 

 found in most growing roots and shoots in embryos, e.g. Quercus, 

 Borrago; in most germinating embryos in pulvini, e.g. Robinia, 

 Mimosa and in the gland cells of the leaves of such insectivorous 

 plants as Sarracenia and Utricularia 1 . Lastly it occurs in very 

 large quantities in galls and other pathological tissues. As far as 

 I am aware the endosperm does not contain tannin, and even in 

 such seeds as Areca Catechu, where the tannin is of officinal im- 

 portance, it is in the cells of the testa, and not of the endosperm 

 that the tannin is present. 



We are now in a position to consider the probable significance 

 of tannin. It is to Sachs 2 that we owe "such knowledge as we 

 possess," as to the probable function of this substance, and he it 

 was who first made any important generalisations with regard to 

 it. He showed that in germinating seeds tannin soon appeared 

 in the cells even though absent before germination had com- 

 menced, or if as in Quercus — where the embryo had already 

 attained large dimensions, — some tannin was already present ; that 

 the quantity rapidly increased. He also noticed that in growing 

 organs tannin was rapidly produced, and remarked 3 that it was in 

 fact formed in the immediate neighbourhood of those parts of 

 the plant in which metabolism was most active. The general 

 occurrence of tannin in leaves further illustrates this statement. 



But what appears specially to confirm Sachs' views and to give 

 the true clue to a satisfactory solution of the question of the physio- 

 logical bearing of tannin is the occurrence of this substance in 

 irritable and pathological tissue. Thus in pulvini, such as that of 

 Mimosa pudica, very large quantities of tannin are present, and its 

 formation appears to be in some way connected "with the irritability 

 of the protoplasm of these organs of movement. In the young 

 and fully formed pulvini, at first none is present, but soon after the 

 movements commence, tannin makes its appearance, and steadily 

 increases in quantity until the death of the leaf, when the propor- 

 tion of tannin in the cell sap is very considerable 4 . Moreover the 

 amount of tannin present, appears to bear some direct relation to 



1 F. W Schimper, Bot. Zeit. xl. 1882. 



2 Sachs, Physiologic Veaetale, 1882. 



3 See also Petzold, Ueber die Vertheihtny des Gerbstojfes in Hokyewcichsen. 

 (Dissertation, Halle, 1876). 



4 Pfeffer, Pflanzen physiologie. 





