68 SCIENCE PROGRESS. 



noteworthy that some of them at any rate contain cyanogen 

 compounds, which may well be utilised after the manner of 

 hydrocyanic acid itself as established by Treub. 



Their distribution in the plants appears to follow that of 

 the amygdalin in the Rosaceous group, but very little 

 definitely is known on this head. The enzyme which splits 

 them up is according to Guignard always found in special 

 cells which do not contain the glucoside. 



Very closely allied to the group of the glucosides is 

 that of the tannins, about the importance of which there 

 has been a good deal of controversy. Some of them are 

 no doubt glucosides, yielding among their products of de- 

 composition gallic acid and sugar. Others are apparently 

 not so associated with a carbohydrate group. They are 

 very widely distributed, and often occur not only in parts of 

 plants which are devoted to storage of materials, but in the 

 tissues where active metabolic work is going on. The 

 task of deciding whether or no they serve as reserve 

 materials or as bye-products is consequently not easy. 



The two views have been strenuously supported by 

 different writers. Sachs, while working on the germination 

 of the Scarlet-runner (68) in which tannin is comparatively 

 plentiful, suggests an antithesis between carbohydrates 

 and proteids on the one hand, and the tannins and colour- 

 ing matters on the other, the latter being in his opinion 

 only bye-products. He advances in support of his view the 

 fact that they appear or increase with renewed growth of 

 the embryo, instead of diminishing as reserve materials 

 should do. Their appearance is coincident with the chemical 

 changes in the undoubted reserves which lead to the 

 utilisation of the latter. The same view is advanced by 

 Schell (69), who suggests that in some cases, however, it 

 may be a nutritive product. In the germination of certain 

 oily seeds, chiefly of plants belonging to the Boroginaceae, 

 tannin, which is present in addition to the oil, diminishes 

 in quantity during the germination. In the stem of the 

 mature plant there is during the winter a considerable 

 quantity of tannin which almost vanishes as spring ad- 

 vances. On the other hand he finds in certain almost parallel 

 cases that the tannin accumulates instead of diminishing. 



