Compound Celluloses 153 



way, the origin of the astringent substances or tannins, widely 

 distributed throughout the plant world ; and not only of the 

 tannins, but more generally derivatives of the trihydric phenols. 

 This problem is of the greatest interest both from the chemical 

 and physiological standpoints. It involves varied transitions 

 from aliphatic to cyclic compounds, and a prominent feature 

 of the synthetic activity of the plant, the elucidation of which 

 is the immediate objective of organic chemistry. 



Of the endless variety of excreted products in vegetable growth 

 e.g. essential oils, waxes, alkaloids, and ' aromatic ' products 

 the tannins have specially attracted the attention of physiologists. 

 An important monograph on the subject has recently appeared : 

 Grundlinien zu einer Physiologic des Gerbstoffs, by G. Kraus, 

 Leipzig, 1888. The work contains the results of extensive experi- 

 mental investigation of the origin, distribution, fate, and function 

 of tannins in normal growths. A resume of the evidence shows 

 generally : 



(1) That the tannins are formed in leaves under the same con- 

 ditions as are necessary for general assimilation, but is an inde- 

 pendent process. The tannins thus formed are transmitted through 

 the leaf stalk, and distributed through the permanent structures. 



(2) They are also formed in processes of growth in the dark, e.g. 

 growth of rhizomes, unfolding of buds, &c. 



(3) Also in isolated cells and tissues, where they remain. 



(4) The tannins take no further direct part in plant assimilation 5 

 they are end-products. 



In dealing with the question of the sudden increase observed 

 in passing from the sap to the heart wood of many trees, the 

 author speaks as follows : ' The only satisfactory explanation would 

 be the assumption that the tannin in this case is formed locally, i.e. 

 in the wood-tissue itself, the parent substance being the tissue of 

 the medullary rays and wood-parenchyma. As to the possible 

 mechanism of such a process, however, we are in total darkness.' 

 That, we venture to think, is no longer the case. 



Destructive Distillation. The decomposition of jute 

 by destructive distillation has been specially investigated by 



