374 THE BIOLOGY OF FLOWERING PLANTS 



This is interesting in view of von Hess's (1917) investiga- 

 tions on the colour sense of the bird. The retina of 

 the eye contains yellowish oil drops, and the effect of 

 these is that of viewing an object through a pale orange 

 glass ; the bird is blue colour-blind, but can distinguish 

 red and green. Of 159 ornithophilous flowers Hsted by 

 Werth, 84 per cent, are red, 8 per cent, white, 5 per cent, 

 yellow, and 2*5 per cent, are blue. BrilHant colour contrasts 

 are frequent ; in Strelitzia regina, for instance, orange and 

 blue. The flowers are scentless and produce nectar in great 

 quantities, so much, in some Australian Proteas, that the 

 natives find it worth while to collect it. The nectar is thin 

 and watery. A striking feature is the rigidity of the styles, 

 stigmas, and filaments which are frequently lignified, 

 evidently in relation to the vigour of their visitors. In some 

 cases a stout platform is provided, as in Strelitzia, where a 

 bract serves. The birds usually sip, however, while 

 hovering, and the platform is usually absent. This is well 

 seen in comparing related ornithophilous and entomophilous 

 species. Thus Salvia pratensis has a large lower corolla lip 

 on which the bee alights, while the ornithophilous S. aurea 

 has no lower lip at all. In the leguminous Erythrina indica 

 the keel and wings, so characteristic of the family, are much 

 reduced, the stamens and style being fully exposed and rigid 

 (Fig. 53). Exposure of these organs is a common feature. 

 Sargent (19 18) has made observations on the ornitho- 

 philous flowers of West Australia which support the con- 

 clusions of Werth. Most West Australian plants are visited 

 by birds, which may do very serious damage to the blossom, 

 e.g. of species of Erica and Arbutus. The woody stamens 

 and style prevent this damage to some extent, so that the 

 feature may be regarded as protective, rather than as directly 

 related to pollination. In other cases there is a direct 

 relation between structure and the visit of a bird. The 

 flowers of Loranthus aphyllus are too large to be pollinated by 

 an insect. The small delicate flower clusters of Acacia 

 celastrifolia are pollinated by birds brushing against them, 

 while taking honey from an extra-floral gland on the phyllode, 



