ON THE FLORAL BLUE. 



By P. Q. KEEGAN, LL.D. 



THii origin of a colouring matter is technically termed 

 cbromogen, i.e., the precursor thereof, or the special chemical 

 constituent, whose presence in the corolla is necessary for its 

 production. Most vegetable colorations are derivatives of 

 what is called the aromatic series of organic bodies, and it is 

 known that as certain members of this series produce the 

 magnificent aniline dyes, whose spectacular effects are familiar 

 in theatres, and so on, so also other members of the same 

 series form the origin of the beautiful tints and hues which 

 clothe the flowers of the field and garden. The floral structures 

 (corolla, sepal, and so on), are built up out of a number of chemical 

 constituents, e.g., cellulose, wax, oil, tannin, mucilage, salts, 

 and so on, which may be withdrawn therefrom and separated 

 by chemical methods. The question arises — a most interest- 

 ing one to the inquiring mind — what is the particular com- 

 ponent of this structure to which is due the outcome of that 

 most enchanting adornment, the blue, red, or yellow floral 

 coloration ? We must, by diligent analysis and with inexhaust- 

 ible patience, turn over every clue ; we must test and examine 

 all the constituents, until we find some particular one which 

 unquestionably betrays its relationship to the aromatic series 

 of hydrocarbons aforesaid ; for we are assured that therein 

 will lie the true spring and fountain of all this floral glory. 



We commence the research naturally by studying specimens 

 of plants which bear really true blue flowers, taking care, of 

 course, that we do not mistake a violet or purple corolla for a 

 really blue one. An astute chemist, who is well versed in the 

 analysis of tannic materials, can foretell where such a subject 

 is sure to be found. He knows that such and such orders of 

 plants — for instance, the Rosaceae or the Leguminosae — do not 

 produce blue flowers, and he can assign a reason therefor. 

 On the other hand, he is quite convinced that certain other 

 orders, such as the Campanulaceae or the Gentianaceae, can 

 assuredly do so, inasmuch as that particular constituent 

 called tannin is of a similar kind in each of the latter two 

 orders, but is widely different from that in either of the two 

 former orders. Which is as much as to say, that a kind of 

 chromogen exists in roses and sweet peas which does not 

 exist in gentians or bell flowers, and vice versa. True blues 

 exist in veronicas, salvias, verbenas, basil, solanum, 

 penstemon, nemophila, convolvulus, borage, hound's tongue, 

 and in all the orders allied to Gentianaceae and Compositae ; 

 but not in lupins, vetches, peas, vetchlings, geraniums, holly- 

 hocks, primulas, balsams, flax, and so on. In the blue flowers just 

 mentioned there is a chromogen, i.e., a tannin common to all 

 as detected by chemical analysis, whereas in the non-blues 

 this special substance does not occur. A noteworthy fact or 

 peculiarity is that while one series or order of plants contain- 

 ing this special colour-producing body may exhibit red or blue 

 flowers only in certain species or even in one and the same 

 plant, another series or species with the same chromogen 

 evolves nothing but red or yellow adornments. In fact, in 

 some cases — as, for instance, in begonias — a genus may be quite 

 capable of displaying an azure appanage, but its powers are 

 confined to that of red. 



However, to come to details, it may be mentioned that the 

 parent substance of the blue flower is called caffetannin and is 

 imbibed in every cup of coffee we drink, whereas when we 

 drink tea we merely absorb something concerned in the pro- 

 duction of red camellias, for example. The chemist will 

 inform you that caffetannin exists in somewhat different forms, 

 and has a different composition, perhaps, in different plants. 

 Some say it is a glucoside ; others deny that ; and some others 



again assert that it is a mere mixture of organic acids and 

 other substances. What is beyond question is that it contains 

 in its composition (molecule) more of what are called hydroxyl 

 groups than perhaps any other tannic compound known ; that 

 is to say, that where an atom of hydrogen might be found, an 

 atom of oxygen takes its place. Oxygen is an element essential 

 to the support of animal life, but it is also a supporter of color- 

 ation, yellow for less of it and blue for more of it. Moreover, 

 we can artificially produce a blue compound from caffetannin ; 

 but from any other kind of tannin save one, this cannot be done. 

 We have only to leave a solution of caffetannin freely exposed to 

 the air with a little chalk added, when we see the latter 

 gradually turn green, and then on pouring off the liquid and 

 adding some acid, a red solution is obtained very like the tint 

 of the foxglove corolla, and so on, and which, like it also, may by 

 a certain treatment be changed into a brilliant blue. By a 

 careful application of dilute solutions of an iron and a sodium 

 salt the dilute colourless solution of the same tannin can also 

 be induced to yield a most beautiful and persistent azure 

 liquid. 



In fact, the complete analysis of any plant that contains 

 this tannin reveals in many ways that we are dealing with a 

 powerful colour-evolving substance. Then again, we observe 

 similar phenomena repeated when other plants, perhaps 

 belonging to widely different classes or orders, are taken in 

 hand. But however wide these taxonomic differences, we find 

 invariably one common feature, viz., the capacity to produce a 

 true blue flower. Moreover, this most remarkable feature is 

 absolutely independent of the status of the organism, of the 

 organic perfection or degradation of the species. The 

 gentians, for instance, with their feeble powers of assimilation 

 and their mycorrhiza infestation ; the Compositae deprived of 

 one at least of the chief factors of organic perfection ; the 

 Labiates more perfectioned than the borages or the solanums ; 

 the Ranunculaceae, Liliaceae, and so on, with types repre- 

 sentative of a special kind of organic debasement — all these 

 and more rise to the same high level of floral glory when they 

 unfold and hang out to sun and shower the " soft eye-music " 

 of the flaunting blue. 



In fact, the blue corolla is caused by the comparative 

 strength and completeness of the process of de-assimilation 

 occurring there, and this, no doubt, is also the cause why in 

 some plants a certain kind of tannic chromogen is produced, 

 and not so in others. The protoplasm, in order to eliminate 

 from its molecule a tannin containing six HO groups, would 

 de-assimilate or oxygenise more completely than if it produced 

 a tannin with only four or five HO groups. Also, in 

 Gentianaceae with very numerous ovules, blue flowers of the 

 most brilliant description are frequently exhibited ; in Com- 

 positae with only one ovule they are comparatively rare and 

 never so effective. In the latter case, the de-assimilation is 

 not complete, various volatile oils, resins, and tannoids being 

 a common outcome of the process. It may occur, of course, 

 that the plant itself may produce in its green organs a large 

 quantity of caffetannin — for example, the common yarrow — 

 while the flowers are white or pale pink ; but this apparently 

 does not occur in plants with vigorous powers of reproduction 

 (e.g., gentians) wherein tannoids only appear in stem, leaf, and 

 root, the more complete and final products being found 

 exclusively in the floral parts. Therefore, in accordance with 

 this report herein set forth for the first time in this journal, 

 let gardeners cease from troubling to " evolute " a pure blue 

 flower on a plant incapable of constructing a tannic chromogen 

 containing less than a certain number of hydroxyl groups. 



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