BEES IN RELATION TO FLOWERS. 251 



to render the composite head conspicuous, and 

 attractive to insects. Some varieties, moreover, emit 

 fragrant odours, and thus present further inducements 

 for visitation. It is remarkable that, in these florets of 

 the outer edge, the gay-coloured petals are developed 

 at the expense of the anthers. Consequently, they 

 produce no pollen, and their pistils have no brushes, 

 as there would be no office for them to perform. 

 The bright rays have accomplished their own special 

 purpose, and the florets may well depend on others 

 for pollen. 



Now, as to the great importance of cross-fertilisa- 

 tion in this species, we may quote the experiments 

 made by Dr. Darwin.^ He says : " Two purple- 

 flowered varieties (of cineraria) were placed under 

 a net in the greenhouse, and four corymbs (or 

 bunches of flowers) on each were repeatedly brushed 

 with flowers from the other plant, so that their 

 stigmas were well covered with each other's pollen. 

 Two of the eight corymbs thus treated produced 

 very few seeds, but the other six produced on an 

 average 41 '3 seeds per corymb, and these germinated 

 well. The stigmas on four other corymbs on both 

 plants were well smeared with pollen from the 

 flowers on their own corymbs ; these eight corymbs 

 produced altogether ten extremely poor seeds, which 

 proved incapable of germinating. I examined many 

 flowers on both plants, and found the stigmas spon- 

 taneously covered with pollen ; but they produced 

 not a single seed. These plants were afterwards left 

 uncovered in the same house, where many other 

 cinerarias were in flower; and the flowers were 

 1 See Cross and Self-Fertilisation of Plants, p. 335.. 



