70 SCIENCE PROGRESS. 



is present in greater or less amount, and noted the changes 

 in the amount present in winter and in spring in their various 

 tissues. He concludes that in no case is there noticeable a 

 diminution of tannin in early winter as starch accumulates, 

 and there is no sign that the starch is formed at the expense 

 of the tannin. When growth recommences in the spring, 

 instead of tannin disappearing from the older tissues it makes 

 its appearance in quantity depending on the amount of 

 growth. The tissues of the bud are commonly crowded 

 with it. Hillhouse's experiments proceeded upon three 

 lines. In the first place plants or parts of plants rich in 

 tannin were made to grow under conditions in which assim- 

 ilation of C0 2 was impossible ; a second set of experi- 

 ments consisted of germinating in darkness seeds containing 

 tannin ; and finally corms were investigated to see whether, 

 as their nutritive material was transported to the newly- 

 formed corm springing from them, tannin was transferred 

 together with the starch. 



In no case was any diminution or transference found, 

 except in the case of Pinus sylvestris already alluded to, 

 when the probability of the tannin being an antecedent of 

 the resin became evident. 



Those tannins which are undoubtedly glucosides must, 

 however, be of some nutritive value, as they give off sugar 

 on decomposition taking place. There is some evidence to 

 show that during the ripening of certain fruits part of the 

 sweetness is derived from an astringent principle resembling 

 and probably identical with tannin, which diminishes in quan- 

 tity as the fruit matures (72). 



A similar uncertainty as to its physiological meaning 

 must for the present be associated with phloroglucin and 

 the compounds into which it enters, which are to be re- 

 garded as ethers corresponding to glucosides. There are 

 two classes of these compounds, which have been described 

 as phoroglucides and phloroglucosides respectively. The 

 former include such bodies as hespentine, phloretine, etc., 

 while the latter, which contain a sugar group in their for- 

 mula, embrace aurantine, rhamnine, hesperidine, etc. They 

 are somewhat difficult to localise, as the reactions they give 



