SLIPPERY SURFACES. 53 
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 firma, 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 
