XI THE SPECIAL COLOURS OF PLANTS 317 



brownish flowers, some of which smell like carrion, are 

 attractive to flies, as the Arum and Aristolochia ; while the 

 dull purj^lish flowers of the Scrophularia are specially attrac- 

 tive to wasps. 



5. Some flowers have neither scent nor nectar, and yet 

 attract insects by sham nectaries ! In the herb-paris (Paris 

 quadrifolia) the ovary glistens as if moist, and flies alight on it 

 and carry away pollen to another flower ; while in grass of 

 parnassus (Parnassia palustris) there are a number of small 

 stalked yellow balls near the base of the flower, which look 

 like drops of honey but are really dry. In this case there is 

 a little nectar lower down, but the special attraction is a 

 sham ; and as there are fresh broods of insects every year, it 

 takes time for them to learn by experience, and thus enough 

 are always deceived to efl*ect cross- fertilisation. ^ This is 

 analogous to the case of the young birds, which have to learn 

 by experience the insects that are inedible, as explained at 

 page 253. 



6. Many flowers change their colour as soon as fertilised ; 

 and this is beneficial, as it enables bees to avoid wasting time 

 in visiting those blossoms which have been already fertilised 

 and their nectar exhausted. The common lungwort (Pul- 

 monaria officinalis), is at first red, but later turns blue ; and 

 H. Miiller observed bees visiting many red flowers in 

 succession, but neglecting the blue. In South Brazil there 

 is a species of Lantana, whose flowers are yellow the first day, 

 orange the second, and purple the third ; and Dr. Fritz 

 Miiller observed that many butterflies visited the yellow 

 flowers only, some both the yellow and the orange flowers, 

 but none the purple. 



7. Many flowers have markings which serve as guides to 

 insects ; in some cases a bright central eye, as in the borage 

 and forget-me-not ; or lines or spots converging to the centre, 

 as in geraniums, pinks, and many others. This enables 

 insects to go quickly and directly to the opening of the 

 flower, and is equally important in aiding them to obtain a 

 better supply of food, and to fertilise a larger number of 

 flowers. 



8. Flowers have been specially adapted to the kinds of 



^ Miiller's Fertilisation of Flowers, p. 248. 



