4 o SLIPPERY SURFACES. [CHAP. 



On the other hand, where the. same object is 

 effected by slippery surfaces, the flowers are often 

 pendulous ; creeping creatures .being thus kept out of 

 them, just as the pendulous nests of the weaver-bird 

 are a protection from snakes and other enemies. 

 As instances of this kind, I may mention the common 

 Snowdrop and the Cyclamen. 



Many flowers close their petals during rain, and this 

 is obviously an advantage, since it prevents the honey 

 and pollen from being spoilt or washed away. I have 

 elsewhere suggested that the so-called " sleep " of 

 flowers has reference to the habits of insects, on the 

 ground that flowers which are fertilised by night- 

 flying insects would derive no advantage from being 

 open in the day ; while, on the other hand, those 

 which are fertilised by bees would gain nothing by 

 being open at night. I confess that I suggested this 

 with much diffidence, but it may now, I think, be 

 regarded as well established. 1 



Silene nutans (Fig. 34), the Nottingham Catchfly, is 

 a very instructive species from this point of view, and 

 indeed illustrates a number of interesting points in the 

 relations between plants and insects. Its life history 

 has recently been well described by Kerner. The 

 upper part of the flowering stem is viscid ; from which 

 it has derived its English name, the Nottingham 

 Catchfly. This prevents the access of ants and other 

 small creeping insects. Each flower lasts three 

 days, or rather three nights. The stamens are ten in 

 number, arranged in two sets, the one set standing in 



1 The so-called sleep of leaves is a different problem, and probably 

 enables the plant to support better the cold of night. 



