198 NATURAL SCIENCi: [March 



same cells where phloroglucin can be detected, tannin-reactions also 

 take place ; but the reverse was not the case, as many cells contain 

 tannin without phloroglucin being present therein. On the whole, 

 Waage concluded that phloroglucin takes part in the formation of 

 phlobaphenes, tannin-reds, and, besides the tannin acid, it has a 

 share also in the brown colouration of dead or dying autumn leaves. 

 Although the researches just mentioned were conducted mostly 

 after the micro-chemical method, nevertheless their vast range and 

 extraordinary minuteness of detail have supplied results which have 

 proved of the utmost value to all practical students of this interest- 

 ing theme. Nothing could be more suggestive than to be apprised 

 regarding the precise distribution of phloroglucin, to know that it 

 exists in one plant and does not exist in another, and sowise to lean 

 gradually to the understanding that, although its function in the 

 formation of certain red colouring matters stands pre-eminent, yet 

 there are certain other red pigments with the origin of which it has 

 got nothing whatever to do. It does not require a specially delicate 

 eye for colour to see that the red of the rose is different from that 

 of the foxglove, that of the rhododendron from that of the daisy, etc. , 

 and such being the case, it is reasonable to surmise or conclude that 

 they have a different origin. What then does there remain for us 

 to state or summarise with respect to the precise chemical causes 

 which bring about the outcome of these brilliant red and blue 

 phenomena of the vegetable kingdom ? In a general way it may be 

 admitted as established that, in Dicotyledons at least, where the red 

 colour of flower or leaf verges towards bluish, as for instance in the 

 rose and rosaceae generally, there the phloroglucin group enters into 

 the molecule of the chromogen ; where, on the other hand, the red 

 is more scarlet, the chromogen seems to be of the nature of an acid, 

 and the actual visible pigment is only a saline compound modified 

 by exposure to the air and by certain substances gums, mucilages 

 which accompany it and even possibly give origin to it. Both forms 

 of tannic chromogen arise from a carbohydrate which, according to 

 its chemical component and constitution, gives origin to certain 

 intermediate tannoid compounds which seem to form, on the one 

 hand, phloroglucin-tannin, and on the '^other, protocatechuic acid- 

 tannins. The former class of tannins when oxidised or dehydrated 

 produce the actual crimson colouration, and for this purpose they do 

 not require to enter into combination with a base ; the change seems 

 to depend on what in chemical parlance is termed condensation, i.e., 

 the formation of an oxide or simple ether by the elimination of HgO 

 I)etween two HO groups in different molecules. It has been surmised 

 that the action is analogous to the action of aldehydes on phenols in 

 the presence of dehydrating agents, as Lindt had originally stated 

 (see above), but experiments conducted with phloroglucin, various 



