12b THK ORCHID WORLD. 



THE COLOURS OF FLOWERS. 



ALTHOUGH a vast amount of informa- 

 tion has been obtained concerning 

 ^ the many physiological problems of 

 plant life, that relating more especially to the 

 formation of colour in flowers has remained 

 somewhat m the background. This is mainly 

 on account of the difficulties encountered m 

 investigating the minute quantities that are 

 oftentimes sufficient to form an intense 

 pigment, and the factors that may completel)- 

 change the colour of the whole flower or any 

 particular section. Colour production is a 

 bye-product of the great utilitarian process of 

 life. 



The different colours of flowers are due to 

 the varying colour of the cell sap, to the 

 different distribution of the cells containing 

 the coloured cell sap, and also to the various 

 combinations of dissolved colouring matter 

 with the yellow, orange or red chromoplasts 

 and the green chloroplasts. The sap pigments 

 may range from blue to red, but the plast 

 pigments are never blue, their colour ranging 

 from bright yellow to bright red. 



At the meeting of the Scientific Committee 

 of the Royal Horticultural Society, Feb. 2nd, 

 191 5, Dr. F. Keeble, F.R.S., in giving an 

 account of the chemistry of flower colours, 

 showed, by means of various experiments, how 

 the sap colours, viz., blue, red, magenta and 

 junk, may be produced. Colourless bodies, 

 called chromogens, are lij^erated from the 

 living substance of the plant, and these when 

 united with oxygen form various pigments. 

 Coloration is an oxidation phenomenon. 



An important factor is the rate and extent 

 of the oxidation, this depending upon the 

 constitution of the cells situated m various 

 parts of the flower. Delay in development 

 frequently occurs, which suggests a reason 

 why some flowers do not always assume their 

 normal colour, but stop, as it were, in an 

 unfinished condition. Richly coloured blooms 

 generally result after a period of suitable 

 growing conditions, while the production of 

 whitish flowers on young or starved plants, 

 which yield coloured ones under normal 

 conditions, is probabl\- due to lack of 



[March, 191 5. 



chromogen and the oxidising agent. Thus 

 we can understand how the light, heat and 

 moisture of one season has its effect on the 

 flowers produced during the following season. 



Close observation of many coloured flowers 

 will detect a beautiful system of venation, 

 which is usually of a richer or darker colour 

 than the general substance of the flower. 

 Until recently these veins have been held 

 responsible as the means by which the colour 

 pigment is brought up from the plant and 

 diffused over the flower. Dr. Keeble, however, 

 does not entirely hold with this view, but 

 believes the veins pour out some material 

 necessary for the process of coloration, and 

 without which the chromogen, the mother 

 of pigment, is unable to make further 

 development. 



Many coloured flowers have white patches 

 where there are present both chromogen and 

 its oxidising agent, but which fail to produce 

 colour owing to the presence in the sap of a 

 third substance having an inhibiting or 

 paralysing effect on the process of oxidation. 



While there are some flowers which are 

 true albinos solely because they entirely lack 

 chromogen, the mother of pigment, and so are 

 unable to make colour, there are others that 

 owe their pure whiteness to the counteracting 

 or paralysing factor, which, so long as it 

 remains, will always prevent the formation of 

 colour in any seedlings that may be obtained 

 hy the use of such jilaiits as parents. 



ODONTOGLOSSUM 

 EDWARDIMIUM. 



Another addition to the already long series 

 of Edwardii crosses has been made by Messrs. 

 Armstrong and Brown, whose success at 

 present is astonishing and most pleasing. 



It is described accurately by calling it a 

 glorified Edwardii, of intense deep purple, 

 with lighter margins to the sepals and petals, 

 the colour being the same both back and front. 



The lip, column and ovary are all exactly 

 the same colour, the anther cap being white. 

 The only things wanting are size and a 

 good lip. 



B. Craix'shay, Roscficld , l-'cb. Sth, igiS- 



