THE COLOURS OF FLOWERS 45 



As to the cause of the greater intensity of colour 

 found in many Alpine flowers, it is not possible to 

 conclude finally at present. There are two alter- 

 natives. Either it is due to the greater intensity of the 

 illumination, or it may be a special adaptation among 

 Alpines to serve as an insect advertisement. There is 

 much to be said for both theories. Prof. Bonnier has 

 made experiments subjecting various plants, under 

 suitable conditions and with necessary precautions, to 

 the influence of a strong continuous light. He finds 

 that the chlorophyll, or green colouring matter of 

 the leaves, is thereby rendered more intense, and 

 the chlorophyll grains more numerous and more 

 evenly distributed. If this is the case with chloro- 

 phyll, it may also be the same with the pigment 

 granules in the petals. In many flowers, especially 

 those with yellow, orange-yellow, or orange-red 

 corollas, the pigment is solid and in the form of 

 granules, or, to state it more accurately, is contained 

 in minute specialised portions of the protoplasm 

 (p. 9) called chromoplastids, just as chlorophyll 

 (p. 10) is also held in small specialised protoplasmic 

 bodies. In a large number of red, blue, and purple 

 flowers, however, and also in some yellow flowers, the 

 pigment is held in solution in the cell sap. 



On the other hand, it is known that there is a 

 larger percentage of flowers which are cross-pollinated 

 by means of insects, especially by butterflies, in the 

 Alps than in the plains. Some of these flowers are 

 specialised to certain groups of insects — that is, they 



