STRUCTURE AND NATURAL HISTORY 3 



have showy flowers. Many plants are entirely sterile 

 with pollen from the same individual, and, whether it is 

 necessary or not, it is always of advantage that pollen 

 should come from another individual plant. 



To carry out this transference of pollen, Irises usually 

 engage the service of bees. It is said that our own 

 " Yellow Flag*" was originally adapted for bees, as its 

 dimensions show, but that since, to a great extent, it has 

 become adapted for flies (Rhingia). 



Take an Iris flower and observe that a bee, of the 

 right size, pressing in (to extract honey) below the 

 arch of the style-arm must necessarily sweep off, on its 

 back, some of the pollen from the anther, which is 

 exactly placed for the purpose. Then observe that this 

 bee, on entering another flower, must necessarily leave 

 some pollen on the stigmatic lip, which is exactly placed 

 so as to be most sure of sweeping it off. The arrange- 

 ment is remarkably perfect, it is a great achievement in 

 evolution, and its existence compels belief in the neces- 

 sity of the function which alone it is designed to meet. 



