xxiv INTRODUCTION 



the column is elongated into a beak that projects over the 

 stigma. This projection is called the rostellum. 



The pollen is never of the dry, dusty sort that blows from 

 tree to tree, nor is it even the brilliant pov^dered gold that is 

 poured forth from the long anther sacs of the lilies. It is 

 gathered in waxy masses that cohere in lumps or clubs, 

 called pollinia, and are generally carried away as a whole by 

 the insect visitors, for with very few exceptions the orchids 

 are wholly dependent upon insects for their perpetuation 

 through seed. They possess no possible resource for self 

 fertilisation if they fail to attract the insects that are especially 

 adapted to enter their honey-throated blossoms. Hence 

 this display of stripes and fringes, of brilliant colours, and of 

 long horns of nectar swung beneath the lip to entice the 

 useful visitors. 



Many common wild flowers that are arranged with 

 special reference to cross fertilisation, can nevertheless 

 fertilise themselves if they do not receive pollen from other 

 plants, and although they do not as a rule set so many or 

 such heavy seeds as if they had been cross fertilised, yet 

 they are not threatened with extinction if they have to 

 depend on their own pollen. The orchids have no such 

 provision, and would never mature their seeds did they not 

 receive pollen from neighbouring plants through the medium 

 of insect visitors. 



It was because of this fact that Darwin chose the orchids 

 as the exponent of his theory of cross fertilisation with 

 which he astonished the world in 1859. 



