194 OUR INSECT FRIENDS AND FOES 



be brought into contact with the stigma. Now 

 although the surface of the stigma is very viscid, 

 it is not so viscid as to pull the whole mass of 

 pollinium off the insect's head, but is just 

 sufficiently adherent to break the elastic threads 

 by which the packets of pollen-grains are tied 

 together, and retain some of them on the stigma. 

 Thus the bee may visit successively several 

 orchid flowers, and fertilize each with some of 

 the pollen-grains from the pollinia attached to 

 its head. 



Many and truly remarkable are the contri- 

 vances existing among our British Orchids, for 

 obtaining the help of insects in their pollination, 

 but even more wonderful are the methods of a 

 tropical Orchid called Catasetum, which the late 

 Charles Darwin considered " the most remarkable 

 of all Orchids." Lord Avebury gives the follow- 

 ing brief and clear description of this wonderful 

 flower : " In Catasetum, the pollinia and the 

 stigmatic surfaces are in different flowers, 

 hence it is certain that the former must be 

 carried to the latter by the agency of insects. 

 The pollinia, moreover, are furnished with a 

 viscid disk, as in Orchis, but the insect has no 

 inducement to approach, and in fact does not 

 touch, the viscid disk. The flower, however, is 

 endowed with a peculiar sensitiveness, and 

 actually throws the pollinium at the insect. 

 Mr. Darwin has been so good as to irritate one 

 of these flowers in my presence : the pollinium 

 was thrown nearly three feet, when it struck 

 and adhered to the pane of a window. This 

 irritability, however, is confined to certain parts 



