28 The Study of Animal Life part i 



have in some districts driven away the titmice and thus 

 favoured the survival of injurious caterpillars. 



5. More Complex Interactions. — The flowering plants 

 and the higher insects have grown up throughout long 

 ages together, in alternate influence and mutual per- 

 fecting. They now exhibit a notable degree of mutual 

 dependence ; the insects are adapted for sipping the 

 nectar from the blossoms; the flowers are fitted for 

 giving or receiving the fertilising golden dust or pollen 

 which their visitors, often quite unconsciously, carry from 

 plant to plant. The mouth organs of the insects have 

 to be interpreted in relation to the flowers which they 

 visit ; while the latter show structures which may be 

 spoken of as the " footprints " of the insects. So exact is 

 the mutual adaptation that Darwin ventured to prophesy 

 from the existence of- a Madagascar orchid with a nectar- 

 spur 1 1 inches long, that a butterfly would be found in the 

 same locality with a suctorial proboscis long enough to 

 drain the cup ; and Forbes confirmed the prediction by 

 discovering the insect. 



As information on the relations of flowers and insects is 

 readily attainable, and as the subject will be discussed in 

 the volume on Botany, it is sufficient here to notice that, so 

 far as we can infer from the history half hidden in the 

 rocks, the floral world must have received a marked impulse 

 when bees and other flower-visiting insects appeared ; that 

 for the successful propagation of flowering plants it is 

 advantageous that pollen should be carried from one indi- 

 vidual to another, in other words, that cross-fertilisation 

 should be effected ; and that, for the great majority of 

 flowering plants, this is done through the agency of insects. 

 How plants became bright in colour, fragrant in scent, rich 

 in nectar, we cannot here discuss ; the fact that they are so 

 is evident, while it is also certain that insects are attracted 

 by the colour, the scent, and the sweets. Nor can there be 

 any hesitation in drawing the inference that the flowers 

 which attracted insects with most success, and insects which 

 got most out of the flowers, would, ipso facto, succeed better 

 in life. 



