134 Flowers and their Unbidden Guests. 



exhaled from eight o'clock in the evening till about 

 three in the morning, together with the white colour 

 of the petals, which is most striking in the dusk, 

 attracts numerous insects that search for nectar 

 in the evening or by night. Such of these insects 

 as are wingless are altogether debarred from access 

 by the viscid matter on the peduncles;^ but flying 

 insects are highly welcome, and to them the honey at 

 the bottom of the flower is willingly offered in exchange 

 for the cross-fertilisation to which they conduce. In 

 the daytime it is quite otherwise. No insect, winged or 

 not, is now welcome to the nectar. The filaments are at 

 this time rolled back, and the anthers have fallen off, 

 or, if still hanging to the filaments, are shrivelled and 

 empty. There is now no poUen in the flowers to be 

 rubbed off, and therefore there can be no fecundation of 

 the stigma. Should the nectar therefore be consumed, 

 it would be expended in vain; and the flowers moreover 

 would be at this further disadvantage, that when even- 

 ing came on they would be nectarless, and therefore 

 would remain unvisited. 



Now to prevent the nectar from being thus stolen 

 without profit, and to protect the flowers from such 

 insects as are active in the sunshine, no better means 

 could be devised than those which are in fact adopted, 



1 See pp. 60, 61. SUene nutans is also very remarkable on 

 another account, namely, as producing tetramorphic flowers. This, 

 however, is a point which I shall have an opportunity of dealing 

 with elsewhere. 



