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



only is none such universal, but the numerous quarries which 

 honeycomb their area, their tough and uniform texture, and above 

 all, the quality of the paving-stones which they furnish are proofs 

 that none such in general exists. These rocks are posterior to the 

 foliation of the gneiss. 



Thus then Ansted's assertion is not only unsupported by, but 

 opposed to evidence. It is possible that he was misled by a sup- 

 posed correlation with the rocks of Sark. But there seems no use 

 in conjecturing the origin of a mistake. Besides the mistake in 

 my opinion extends far wider and deeper. I believe these northern 

 rocks of Guernsey to be as a whole igneous, and eruptive. The 

 evidence of this will be given in a paper which is in process of 

 preparation. 



May 28, 1883. 



Mr Glaisher, President, in the Chair. The following 

 communications were made to the Society : 



(1) On the general occurrence of Tannins in the vegetable cell 

 and a possible view of their physiological significance. By W. 

 Gardiner, B.A. 



In the following paper I propose to consider as briefly as 

 possible, the chemical nature of tannins, their occurrence, and 

 what appears to be their physiological bearing in the general 

 economy of the plant 1 . 



Under the head of tannins have been grouped a number of 

 bodies which as far as our limited knowledge of them goes may 

 be conveniently classed together, both on account of their general 

 properties and reactions. Thus they have an astringent taste ; 

 a slightly acid character; they precipitate albumen and gelatin 

 and give with ferric chloride either a blue black or a green 

 colouration or precipitate. Most of them are glucosides being 

 resolved by ferments or by heating with dilute acids into tannic, 

 and finally into gallic acid, and glucose, and on fusion with potash 

 yield in nearly every case protocatechuic acid and phloroglucin. 

 They must consequently be regarded as aromatic glucosides. 



Our knowledge as to the chemistry of the tannins has advanced 

 but little since Sachs in his Physiologie Vege'tale of 18G5 w r rote 

 " The physiological character of tannin can only be studied with 

 any advantage when chemists have taught us something certain 

 about its relations with other substances." All tannins were at 



1 The whole literature of tannin has been collected by Kutscher in bis paper 

 "Ueber die Verwendung der Gerbsaiire im Stoffwechsel der Pflanze." Flora 

 4. 1883. 



