THE DICOTYLEDONES 



1963 



of the spherical inflorescences downwards. The corolla of the tubular 

 florets is divided almost to the base into five slender, bright blue 

 lobes which spread out above like a star. The lower portion forms 

 a spherical reservoir for nectar which is partly protected from rain 

 by the hairy margins of the petals. The tip of the style is densely covered 

 with short hairs which push out and hold the pollen grains while a further 

 circle of much longer hairs later removes it from the tubular corolla. 

 At this time the inner surface of the stylar arms is quite undeveloped and 

 it is only several days after the pollen has been discharged that the receptive 

 papillae develop. By this time the pollen has been removed either by insects 

 or by wind and the corolla lobes now bend inwards and surround the style, 

 leaving the stigmas ex- 

 posed and isolated. It 

 follows therefore that in 

 this case only cross- 

 pollination is possible. 



Our second example 

 is Centaur ea cyainis (Fig. 

 1892) (Cornflower). In 

 this case the ray florets 

 are neuter, funnel-shaped 

 and radiating while the 

 disc florets are hermaph- 

 rodite and tubular. Below 

 the short, broad stylar 

 branches is a ring of 

 sweeping hairs which are 

 directed upwards. The 

 nectar is secreted in the 

 base of the corolla and 

 when the proboscis of a 

 visiting insect is inserted 

 to probe for nectar the 

 filaments of the anthers 

 contract rapidly and the 

 pollen is swept out and 

 carried off by the insect. 

 At this stage only cross- 

 pollination is possible. 

 Later the stigmatic lobes 

 of the style bend back 

 sufficiently to come into 

 contact with pollen ad- Fig. i892.-Ce«^n/m/nvm»5 Cornflower. A and B, 



. '^ . Details of the sweeping hairs on the style. L-, 



hermg to the Sweepmg Stvle still enclosed within the tube formed of the 



hairs, so that self-pollin- api^al extensions of the anthers in which the 



'. . / pollen collects. D, Stvle finallv emergent, 



ation is now possible. 1 he See in text. 



