THE RESERVE MATERIALS OF PLANTS. 



( Concluded. ) 



THE position of the glucosides in vegetable metabolism 

 has been for a long time a subject of considerable 

 controversy, which has, however, been most largely con- 

 cerned with tannin. The details of its formation, its locali- 

 sation and its fate have been discussed at great length, but 

 the discussion has been largely conducted on the lines of 

 hypothesis and analogy rather than experiment. The con- 

 clusions reached by such a method of treatment have some- 

 what hastily been applied to all glucosides, as if tannin were 

 eminently the typical one. There are now reasons for 

 thinking that so far from this being the case it is especially 

 exceptional. 



The number of oflucosides known has increased con- 

 siderably in recent years as our investigations into plant 

 metabolism have been pursued, and increasing knowledge 

 of them forces the conviction more and more upon us that 

 they take a more or less active share in the nutritive pro- 

 cesses, possibly direct, but more probably through certain 

 of the products to which they give rise on decomposition. 

 They are not so markedly reserve stores for seeds as are 

 many of the bodies we have already discussed, though many 

 seeds, and notably many of those of plants of the Rosaceae 

 and Cruciferse and orders allied to these, contain them in 

 quantity together with other reserves. They occur, how- 

 ever, in other parts of the plant, not quite as circulating 

 reserves, but rather as transitory stores for more localised 

 growth and nourishment. The old advocates of their 

 nutritive functions rested their case largely on the presence 

 of sugar in the glucoside molecule, and held that this is the 

 body which is available for the constructive processes of the 

 organism. There are, however, reasons for holding that 

 this view is too limited a one. and that some of the other 

 products of their decomposition may be as valuable as the 

 sugar, if not of even greater importance. 



