182 COLOURS OF FLOWERS AS A MEANS OF ATTRACTING ANIMALS. 



The flowers of the Phygelius capensis (illustrated in fig. 251 3 ) show at the base 

 of the tubular corolla a small expansion filled with honey which is converted into 

 a closed cavity by the ovary bending down in front of it and pressing itself closely 

 to the wall of the corolla-tube. In the flowers of Tricyrtes pilosa (see fig. 251 4 ), 

 whose three outer perianth-leaves secrete honey in the expansion at the base of 

 the flower, the three-sided ovary is wedged in like a prop between the perianth- 

 leaves, and three closed nectaries are thus formed out of the expansion. A similar 

 appearance is also observed in the flowers of Hypecoum procumbens. Here the 

 honey is secreted in a pit close above the claw of the two inner petals (see fig. 

 25 1 5 ). Just as in Ranunculus glacialis, so here, this pit is covered by a peculiar 

 scale which is fitted to receive the pollen at a certain stage of development, as will 

 be afterwards described. This scale is erect and parallel to the ovary, its base 

 being in contact with it (cf. fig. 251 6 ). In this way the pit or nectary is completely 

 closed in. 



It may be remarked finally that in many cases the stigma may act as a covering 

 to excavated, honey-containing flowers. This is so, for example, in the Gentians 

 of the group Cyclostigma, the flower and stigma of one species of which (Gentiana 

 Bavarica) are illustrated in figs. 25 1 1 and 25 1 2 . 



THE COLOUES OF FLOWEKS CONSIDERED AS A MEANS OF 

 ATTEACTING ANIMALS. 



If we wish that certain distant objects should be plainly seen, it is usual, as 

 is well known, to assist the eye by contrasts of colour. We place signals on the 

 railways with a red band on a white background, put gold letters on black sign- 

 boards, and paint a black circle and a black spot on the white disc towards which 

 we point the gun. The same colour-contrasts occur in plants whose flowers are the 

 aim of flying animals. 



Since flowers in most cases open above green foliage-leaves, it is evident why 

 in the floral region those colours are most often met with as allurements which 

 contrast well with green. Of those plants of the Baltic flora whose flowers are 

 displayed against a background of green, 33 per cent are white, 28 per cent yellow, 

 20 per cent red, 9 per cent blue, 8 per cent violet, and 2 per cent brown. Looked 

 at from a distance white, yellow, and red stand out best from the green of the 

 foliage, blue and violet only a little, and brown scarcely at all. 



Usually it is the petals whose colour standing out from the surroundings makes 

 the flowers conspicuous from a distance. That side which is presented towards the 

 flying insects displays the colour most brightly. When the corollas or perianths 

 are pitcher-shaped or bell-shaped, nodding or pendulous, so that the animals on 

 approaching do not see into the inside of the flower, the outside is coloured the 

 more brilliantly. But if, on the other hand, the flower is star-shaped or disc- 

 like, with its face turned to the sky, and to the swarming insects, then the inner 

 side shows the brighter colours. There are even some flowers whose petals are 



