630 The Outline of Science 



is protective. But we have assigned no function to the corolla, 

 that part which, to our aesthetic sense, is the essence of the flower, 

 giving it distinctive form, giving it colour, frequently giving it 

 scent and sweetness. For the nectar glands are in some flowers 

 associated with the petals, though in others with the stamens or 

 ovary. 



The form of the flower, in particular the character of the 

 corolla, is intimately bound up with the pollination, with the 

 means by which the pollen is transferred from the stamens to 

 the stigma. 



The flower is now understood as an arrangement by which 

 pollination is secured. Though the four parts of the flower have 

 different names and forms and uses, they have fundamentally a 

 common nature, for they are all leaves, transformed in various 

 ways and combining to fulfil the plant's chief end that it should 

 produce seeds which will develop into full-grown plants and bear 

 next year's flowers. All the differences in the form and position 

 of the floral parts, which give individuality and character to differ- 

 ent flowers, may be referred to the variety of means employed 

 for securing the transference of pollen, which precedes fertilisa- 

 tion. Perhaps nowhere else in nature can we see so clearly the 

 fineness with which two organisms flowers and their insect vis- 

 itors are fitted to each other. 



But while on the whole the variety of bright flowers corre- 

 sponds to the variety of insects that visit them, or to the different 

 ways in which one insect may work, it is not true that insects 

 alone are important in carrying pollen. There are flowers in the 

 Tropics pollinated by humming-birds ; a few of our native flowers, 

 for example those of the golden saxifrage, are pollinated by 

 slugs; aquatic plants, the grasswrack of the sea as well as the 

 pondweeds and others of fresh water, have water-borne pollen. 

 These are relatively small classes, but rivalling the insect-pollin- 

 ated plants in numbers are all those plants with inconspicuous 

 flowers, trees and grasses, which are pollinated by the wind. 



