168 BRITISH PLANTS 



All flowers were once pollinated by wind ; they were 

 small, green, and inconspicuous. This method, however, 

 entailed tremendous waste of material, and with it all 

 seed-production was uncertain, since pollination was left 

 to chance. When wind, as an agent of pollination, began 

 to be replaced by insects, waste was diminished, and seed- 

 formation became more certain. Provided it possessed 

 adequate material to serve as food for insects, any flower 

 which happened to be a little more conspicuous than its 

 fellows by certain traits of form or colour, or which 

 betrayed its presence to them by some pervading scent, 

 was bound to receive greater attention. Insects would 

 visit it in greater number, and the production of seed 

 would become greater and more certain. Now, this 

 would be a distinct benefit to the plant, and plants so 

 equipped would be better fitted than others to survive 

 in the struggle for existence. This is what has actually 

 happened. Every advance made by the flower in the 

 direction of making it more attractive to insects has been 

 a gain. It has given its possessor an advantage over its 

 competitors which, being less efficient, have been gradually 

 but inevitably ousted from their habitats. 



As plants have specialized in these directions, the 

 pollinating insects have specialized too. Their mechanism 

 of flight has been modifled for rapid and easy movement 

 from flower to flower. They have acquired more skilful 

 means of attachment, and the organs by which they 

 extract honey have developed into wonderful instru- 

 ments of precision. As the corolla-tube became longer, 

 and the honey more and more concealed, their tongues 

 have become longer and more specialized. The evolution 

 of the insect has kept pace with the increasing specializa- 

 tion of the flower and the increasing difficulty in obtaining 

 honey. 



Entomophilous flowers offer two kinds of food to their 

 insect- visitors, and they may be divided into two classes, 

 according to the nature of the food which they offer— 



1. Pollen-Flowers, which contain no honey, and are 

 visited by insects for the sake of the poUen alone. The 

 an thers are large and generally numerous, and the quantity 

 of pollen formed is very great. The poUen is taken home by 

 bees, and kneaded into a kind of pollen-bread for the grubs. 

 PoUen-flowers include the rose, clematis, pseony, marsh- 



