January i6, 190'S] 



NATURE 



261 



optical properties, occasionally by the fluorescence, but 

 usually by the absorption, as studied by a spectrum micro- 

 scope, and whenever possible by the position of absorption 

 bands under identical known conditions. This latter is 

 very important, since their position may vary considerably 

 with the character of the solution. I never attempted to 

 obtain the pigments pure, in a state fit for chemical 

 .inalysis, so as to determine their chemical composition. 



The number of distinctly different colouring matters in 

 flowers must be very great, and to study them completely 

 would occupy a long lime. The distribution of the 

 different kinds is sometimes very definite, but often the 

 reverse. In the genus Hypericum are sometimes small 

 dark spots in the petals, and sometimes small dark 

 rounded bodies are attached to the sepals. These are 

 coloured by a pigment which gives a spectrum with narrow, 

 well-marked absorption bands, which could not be mis- 

 taken for any other. This occurs in all the species I 

 examined, but in no other flowers. On the contrary, there 

 is a blue pigment, giving a sufficiently well-marked spec- 

 trum with several absorption bands, met with in many 

 (lowers separated about as much as possible botanically. 



Much may be learned by the use of reagents. Vegetable 

 piginents may be divided into three groups by the action 

 of sodium sulphide, which I called Groups .A, B, and C. 

 Group A is at once made nearly or quite colourless by the 

 addition of a small quantitv of this salt. Group B is not 

 at all altered when alkaline or neutral, but is at once 

 made nearly colourless when acid. Group C is not 

 changed even when acid. When made colourless the pig- 

 ments are not permanently decomposed, but recover their 

 colour when evaporated to drvness. I do not fully under- 

 stand the cause of these effects. 



Then, again, much mav be learned from the action of 

 citric acid and a weak alkali. The colour and spectra 

 of many reds, purples, and blues are very different in acid, 

 neutral, or alkaline solution. .Some yellow pigments are 

 made thirty times more intense by an alkali, whilst others 

 aj-e unchanged. .As a rule, none of the above changes 

 is due to a permanent alteration, but in some cases it 

 is useful to emplov stronger reagents, which decompose 

 the natural pigments, such as nitrite of soda with the 

 addition of a little citric acid. As an example I may 

 cite the pigment of the common yellow garden crocus. 

 This gives a strongly fluorescent yellow substance, unlike 

 that produced in the case of any other flower I have 

 ixamined. The only objection to such powerful reagents 

 is that they may produce highly coloured substances from 

 colourless bodies in the plant, and not merely alter the 

 coloured constituent. .As an interesting example I may 

 name a deep red substance produced in the case of the 

 different species of geranium examined, but not in the 

 case of any other plant. 



My remarks so far apply only to colouring matters 

 soluble in water. Orange, orange-yellow% and lemon- 

 yellow flowers are in most cases coloured by one or other 

 of the four yellow pigments met with in green leaves, or 

 by various mixtures of them, which are distinguished by 

 the absence or presence of two absorption bands. These 

 vary considerably in position according to the nature of 

 the solvent, lying much nearer the red end of the spectrum 

 wh'-n the pigment is dissolved in carbon bisulphide than 

 when in benzol or alcohol. These absorption bands can 

 also be seen in the spectra of the flowers themselves, and 

 for some time I was unable to understand why in the 

 case of Chelidoniitiii majiis they lay materially nearer the 

 red end than in • nearly all other yellow flowers which 

 gave the same spectrum when the pigment was in solu- 

 tion, until I came to the conclusion that in Chelidonium 

 ii occurs in a free state, and not dissolved in oil or wax. 

 There are other cases in plants where the spectra show 

 that the pigments exist in a solid state, which would ex- 

 plain slight differences in tint. 



W'e may now consider facts very common in cultivalrd 

 plants, viz. a great variety of colours. In many cases 

 this is easily explained, because we can see that two pig- 

 ments exist, either alone or mixed in various proportions, 

 one frequently being a vellow insoluble in water, and the 

 other a blue or red soluble in it. As an example, I refer 

 to the common wallflower of our gardens (Calendula 

 viilgaiis). which is som.-times a clear vellow. sometimes 



a sort of crimson, but more commonly a crimson brown. 

 The yellow is a xanthophyl soluble in carbon bisulphide ; 

 the crimson is a pigment soluble in water ; the common 

 colour is a mixture of these two, and gives the same 

 spectrum as a yellow and a purple petal combined. \\ e 

 have a similar case in chrysanthemums and various other 

 flowers. The common garden marigold is sometimes a 

 pure vellow and sometimes a true orange or an inter- 

 mediate tint, which is due to two different pigments alone 

 or variously mi.xed. One or other of these may occur 

 separate in different parts of the same flower in some 

 plants. 



In some flowers we find a considerable variety of tints, 

 probably due to another cause. The common bedding 

 geraniums of our gardens are a good example of this. 

 .•\t one time I thought that such varying tints might be 

 due to varying acidity, but did not obtain satisfactory 

 proofs, though it may be true in some cases. I, however, 

 studied several closely allied pigments from other plants, 

 and found that they seemed to agree in nearly every 

 particular, except that the absorption bands in the 

 spectra were not exactly in the same place. .An excellent 

 example of this kind is the red pigment of blood, giving 

 two very well-defined absorption bands, which differ in 

 position if the oxygen is replaced by carbonic oxide or 

 nitrous oxide. Also the red pigment found in many birds' 

 eggs, which I named oorhodeine, gives precisely the same 

 remarkable and well-marked spectrum as the product of 

 the action of strong sulphuric acid on the red pigment of 

 blood, except that the position of the absorption bands 

 differs distinctly. My suggested explanation of the difl'er- 

 ence in the colour and spectra of a number of the pig- 

 ments in flowers is that some fundamental constituent is 

 the same, but modified by some varying substance in 

 I combination. 



A few flowers contain pigments which give spectra with 

 unusually well-marked absorption bands. .\s remarkable 

 examples I mav mention the crimson Cineraria and the 

 deep blue Lobelia of our gardens. The spectra are of 

 almost exactly the same character, having two dark 

 absorption bands, only they occur at a different part of 

 the spectrum. I am unable to say whether this shows 

 anv relationship between the pigments, but the difference 

 in the position of the bands is perhaps too great. 



It will thus be seen that a very great number of distinct 

 pigments are found in flowers, sometimes having a very 

 restricted distribution, and sometimes the reverse. Then, 

 again, the plant may be able to form two or more quite 

 distinct colouring matters, either alone or mixed in varv- 

 ing proportions. In some cases the pigments seem to be 

 easilv subject to change, as though some constituent could 

 be substituted for another. In one way or another there 

 is thus great scope for variation, perhaps not brought into 

 plav, or onlv to a limited extent, in wild plants, but some- 

 times to a remarkable extent bv cultivation. 



H. C. Sorry. 



VNIVERSITY AND EDVCATIOXAL 

 INTELLIGENCE. 



C.\MiiUiDGF.. — The \'ice-Chancellor has received a litter 

 from Baron von Hugel, curator of the Museum of General 

 and Local Archaeology and of Ethnology, recording a gift 

 from the Rev. John' Roscoe, of the Church Missionary 

 Societv, of exceptional value and interest. It consists of 

 a second instalment of selected native manufactures from 

 Uganda. The chief value of the gift lies in a unique set 

 of relics of deceased Baganda kings, which, enclosed in 

 ornate cases, were preserved bv the people under the name 

 of Lubare (i.e. the Deity) in 'special shrines placed under 

 the guardianship of hereditary custodians. Of these king- 

 gods, the most sacred objects of Baganda cult, three 

 generations are represented in the present collection. 



With the first Roscoe collection, which was supplemented 

 bv a valuable gift of objects from the Katikiro of Uganda, 

 the Universitv acquired Kibuka, the war god of the 

 Baganda. who with all his appurtenances was safely un- 

 earthed from his ruined shrine in the Mawokota district. 

 In this deitv. as in the Lubare, personal relics form the 

 essentials, and in Kibuka are enshrined the jaw-bone, &c.. 



NO. 1994, VOL. yy] 



