SLIPPERY SURFACES. 63 



surfaces. In this case, also, the leaves often form a 

 collar round the stem, with curved surfaces over which 

 ants cannot climb. ' I have assured myself,' says 

 Kerner, ' not only by observation, but by experiment, 

 that wingless insects, and notably ants, find it impos- 

 sible to mount upwards over such leaves as these. 

 The little creatures run up the stem, and may even 

 not unfrequently traverse the under surface of the 

 leaves, if not too smooth ; but the reflexed and slip- 

 pery margin is more than the best climbers among 

 them can get over, and if they attempt it they invari- 

 ably fall to the ground. There is no necessity for the 

 lamina of the leaf to be very broad ; even narrow 

 leaves, as, for instance, those of Gentiana firman are 

 enough for the purpose, supposing, of course, that the 

 margin is bent backwards in the way described.' 



Of this mode of protection the cyclamen and snow- 

 drop offer familiar examples. In vain do ants attempt 

 to obtain access to such flowers, the curved surfaces 

 baffle them ; when they come to the edge they inevit- 

 ably drop off to the ground again. In fact, these 

 pendulous flowers protect the honey as effectually 

 from the access of ants, as the hanging nests of the 

 weaver and other birds protect their eggs and young 

 from the attacks of reptiles. 



In a third series of plants the access of creeping 

 insects is impeded or altogether prevented by certain 

 parts of the flower being crowded together so as to 

 leave either a very narrow passage or none at all. Thus 



