154 THE BEAUTIES OE NATtJRE ' chap. 



Now it is obvious that flowers which, are 

 fertilised by night-flying insects would derive 

 no advantage from being open by day ; and 

 on the other hand, that those which are 

 fertilised by bees would gain nothing by 

 being open at night. Nay it would be a 

 distinct disadvantage, because it would render 

 them liable to be robbed of their honey and 

 pollen, by insects which are not capable of 

 fertilising them. I have ventured to suggest 

 then that the closing of flowers may have 

 reference to the habits of insects, and it may 

 be observed also in support of this, that wind- 

 fertilised flowers do not sleep ; and that many 

 of those flowers which attract insects by 

 smell, open and emit their scent at particular 

 hours ; thus Hesperis matronalis and Lychnis 

 vespertina smell in the evening, and Orchis 

 bifolia is particularly sweet at night. 



But it is not the flowers only which 

 " sleep " at night ; in many species the leaves 

 also change their position, and Darwin has 

 given strong reasons for considering that the 

 object is to check transpiration and thus tend 

 to a protection against cold. 



