CH. XI] INSECT VISITORS. 153 



Fertilisation by means of insects. 



In order that the egg-cell may be fertilised it is 

 necessary that pollen shall reach the stigma. The 

 question therefore how the pollen reaches this position 

 has to be met, and the flowers of the papilionaceous type 

 are well adapted to illustrate one of the chief means of 

 pollen-distribution, namely by means of the visits of 

 insects. When it is understood that it is advantageous 

 to the species that its flowers should be so visited, we can 

 understand the meaning of many parts of the flower which 

 without the knowledge of this fact would be meaningless. 

 Thus the bright colours and sweet scents of flowers 

 undoubtedly serve to attract insects, while the sugary 

 juice or nectar supplies a more substantial attraction. In 

 the buttercup the scale-like nectary has been described ; 

 in the pea-flower the receptacle is more elaborate, being 

 in fact the trough made by the united filaments. The 

 freedom of the tenth stamen gives the visiting insect 

 access to the nectar, and that this is the meaning of the 

 arrangement is clear from the fact that where (as in the 

 Broom) there is no nectar (the flower being visited by 

 bees for the sake of the pollen), the tenth stamen is united 

 to its nine fellows 1 . 



The flowers of the bean and pea are especially adapted 

 to be fertilised by bees, and the manner in which these 

 insects visit them presents some points of interest. In 

 settling on the flower the bee uses the alae as" a stage to 

 alight on, and these petals being intimately in connection 



* The stamens are then said to be monadelphous, 



