164 THE LESSON OF EVOLUTION 



any importance to a plant that it should be visited 

 only by a particular species of humble bee, or that 

 it should be fertilised at night and not in the day ; 

 and we know that those plants which have the most 

 elaborate apparatus for securing cross-fertilisation 

 by certain insects are uniformly rare ; and have not 

 therefore been a success from their own point of 

 view. Also, if it be good for a plant to have its 

 flowers fertilised by pollen from some other plant, 

 then it is evident that the grouping of flowers into 

 heads or spikes must be injurious, because it almost 

 insures that the flower shall be fertilised by pollen 

 from other flowers of the same inflorescence ; which 

 Darwin says does little or no good ; and yet capitate 

 flowers are abundant. 



Indeed, some of the variations which have taken 

 place are decidedly injurious to the plant, such as 

 the reduction of stigmatic surface in the Orchids, the 

 abortion of one half of each anther in Salvia, and the 

 asexual condition of the ray-florets in some of the 

 Composite, and in the outer florets of the Guelder 

 Rose. As a matter of fact, we find that in some 

 cases these metamorphosed flowers are not suffi- 

 cient to preserve the species from destruction, and 

 they have been supplemented by others which have 

 special means for self -fertilisation. If cross-fertili- 

 sation were all that is wanted, the simple device of 

 dichogamy that is- the maturing of different parts 

 of a flower at different times would have answered 

 every purpose. 



But it is evident that capitate flowers are useful to 

 the insects which visit them ; for that arrangement 



