IOO 
THE COLOURS OF FLOWERS 
red flowers, more or less inclined downwards with long tubes, 
and no landing-places such as occur in insect-flowers, the birds 
hovering before the flowers. In the Indo-Malayan region 
many flowers are visited by sun-birds, but whether they are 
specially adapted to them is not known. These birds often 
spoil the flowers by pecking through the tube. 
Colours of flowers , &c. The subject of the colours of 
flowers — and indeed of colour in plants generally — is one of 
considerable difficulty; we shall only attempt a sketch of 
some of the outstanding facts. The green colour of the 
vegetative organs is due to the presence of chlorophyll in 
certain specialised parts of the cell-protoplasm, known as 
chloroplastids. Green is rarely seen in corollas though there 
are several cases, e.g. Deherainea. The colours most often 
seen are yellowish-green, yellow, red, white, blue, and shades 
of these or intermediate colours ; yellow and white are the 
most common, blue the least so. Yellow flowers nearly 
always possess chromoplastids , protoplasmic bodies containing 
the yellow colouring matter. Some red flowers, and a very 
few blue ones have chromoplastids also. Most red and 
nearly all blue, purple, and violet flowers have the colouring 
matter dissolved in the cell-sap. White flowers have colour- 
less sap and plastids. This difference explains the fact 
that in the variations of colour so often seen, it is exceedingly 
rare for a green or yellow to pass to blue, or the reverse. 
All flowers, whatever their colour, seem to vary most easily 
towards white, and this is not difficult to understand. 
This subject of colour-variation shows many points of interest. 
In the same individual flower, most Boraginaceae vary from red to blue 
as the age of the flower increases; the spots in Aesculus vary from 
yellow to red, the corolla of Myosotis sp. from white or yellow to blue, 
and so on (see Ribes, Fumaria, Diervilla, Arnebia, Cobaea, &c.). In 
some cases the flowers of a given plant differ in colour in different 
years. There are many species which show different colours in different 
flowers ; sometimes these are special varieties or races, sometimes, as in 
Polygala, merely individuals otherwise exactly alike. The most striking 
varieties in colour may be seen in the cultivated forms, but they follow 
the same rules as the wild ; it is found that for each species there is a 
certain range of colour beyond which it cannot be made to go in 
cultivation, and does not go in nature. By hybridisation and in otherhvays 
mixtures of colours may be produced, and every variety of shade and 
sometimes of variegation, but beyond certain limits the species cannot 
be made to pass. These limits are found to be as a rule the colours 
