COLOURS OF FLOWERS AS A MEANS OF ATTRACTING ANIMALS. 193 



the circumference. This phenomenon is most beautifully shown in species of this 



genus which grow in the Taurus {jEthionevia grandiflorum and diastrophis) 



where the white centre of the corymb is surrounded by an ornamental red wreath 



of older, folded flowers. The species of the genus Bitter Cress (Cardamine), which, 



together with many other Cruciferte, form a fifth group, agree with the species 



of Wild Cress just described in regard to the enlargement and folding together of 



the petals, but in them the contrast is not brought about by the juxtaposition of 



the colours on the upper and under sides of the petals, but by a change of colour 



in the sepals. The sepals, originally green, become coloured yellow in the older, 



horizontally-placed flowers, but the colour of the petals remains unaltered, white 



or violet. Finally, in the flowers of a sixth group, of which Kernera suxatilis 



(fig. 252 ") may serve as an example, the petals of the older flowers do not fold 



together and do not adhere to the ovary, but retain the position which they had at 



the beginning of flowering, i.e. they always present the upper side to the beholder. 



But as the flowers get older the ovary swells enormously and becomes coloured a 



dark purple brown; it pushes itself between the petals, and these (which have 



increased considerably) now form a white inclosure to the purple fruit. Thus the 



old flowers at the circumference of the corymb obtain a spotted, conspicuous 



appearance. 



We have now to speak of the colour contrast which comes into play between 



different kinds of plants growing in the same district, the flowers of which unfold 



simultaneously. In a meadow studded with thousands of the blue flowers of the 



Campanida, the orange-coloured stars of Ai'nica montana rising up between them 



show up much more plainly than if these Bell-flowers were not present. The same 



may be said of the Bell-flowers whose blue colour is materially heightened by the 



presence of the orange-coloured stars of the Arnica. It might almost be said that 



the growth of plants side by side with contrasting colour.s so tVequently observed is 



arranged in the way here indicated, and the change of colour in the flowers of one 



and the same species in different regions can also be explained by the fact that 



contrast of colour is so advantageous to the plants in question. Let us suppose 



that on a meadow where in summer a plant with red flowers — perhaps a Pink — 



grows in great quantity, a blue Bell-flower has established itself. Some members 



of it may bear white flowers, as often happens in this plant. Without doubt these 



white Bell-flowers show up better than the blue from the red Pinks, and therefore 



have more chance of being visited by insects and of forming fruit and seeds. In 



coui-se of time the white Bell-flowers will constitute the overwhelming majority, 



and the meadow will be studded for the most part with white Bell-flower blossoms 



growing between the Pinks with their red flowers. If the same Bell-flower had 



established itself in a field in which orange-yellow flowers grew in great numbers, 



the blue and not the white-flowered plants would have been visited by insects, 



since they would be the more conspicuous ; thus they would multiply and ultimately 



prevail. 



In the neighbourhood of the Brenner Campanula Trachelium bears white 

 VOL. II. 63 



