228 TROPICAL NATURE, AND OTHER ESSAYS. 



they may be older than any fruit-eating mammal 

 adapted to feed upon their fruits. The attractive 

 coloured fruits on the other hand, having so many 

 special adaptations to dispersal by birds and mammals, 

 are probably of more recent origin.-^ The apple and 

 plum tribes are not known earlier than the Miocene 

 period ; and although the record of extinct vegetable life 

 is extremely imperfect, and the real antiquity of these 

 groups is no doubt very much greater, it is not im- 

 probable that the comparative antiquity of the fruit- 

 bearing and nut-bearing trees may remain unchanged 

 by further discoveries, as has almost always happened as 

 regards the comparative antiquity of animal groups. 



Attractive Colours of Flowers. — The colours of flowers 

 serve to render them visible and recognizable by insects, 

 which are attracted by secretions of nectar or pollen. 

 During their visits for the purpose of obtaining these 

 products, insects involuntarily carry the pollen of one 

 flower to the stigma of another, and thus efiect cross- 

 fertilization ; which, as Mr. Darwin was the first to 

 demonstrate, immensely increases the vigour and 

 fertility of the next generation of plants. This dis- 

 covery has led to the careful examination of great 

 numbers of flowers ; and the result has been that the 

 most wonderful and complex arrangements have been 

 found to exist, all having for their object to secure that 

 flowers shall not be self-fertilized perpetually, but that 

 pollen shall be carried, either constantly or occasionally, 

 from the flowers of one plant to those of another. 

 Mr. Darwin himself first worked out the details in 

 orchids, primulas, and some other groups ; and hardly 



^ I owe this remark to Mr. Grant Allen, author of Physiological Esthetics. 



