TRACHEATES 2OI 



It would take too long to enumerate all the 

 adaptations of the flowers to insects. The most familiar 

 of all is the meadow-sage. In this the bees in search of 

 honey press on a small mechanism by means of which 

 the filaments, at the tip of which the pollen hangs, bend 

 down on it and dust their hairs with it. The bee then 

 leaves the flower, and another comes which has already 

 been covered with pollen in this way. But in the mean- 

 time the pistil with the stigma, which had up to that time 

 been hidden, has come to the opening. The second bee 

 has to rub its body against the stigma in order to reach 

 the honey, and so cause fertilisation. 



We thus see that the origin of the flowers affords a 

 striking proof of the power of natural selection, and this 

 will be particularly clear if we consider the relative 

 imperfectness of the adaptations. Selection only acts 

 in so far as a change is urgently necessary for the 

 preservation of a species. Many flowers can only be 

 fertilised by bees, but they also receive the visits of 

 many other insects which rob them of their honey with- 

 out doing them any service. However, it is clear that 

 further contrivances for excluding these other insects are 

 not necessary, because the maintenance of the species is 

 sufficiently assured by the bees, whose visits are frequent 

 enough to fertilise and bring new plants into existence. 



The alteration of the flowers was bound to have an 

 influence on the insects. When those of the flowers 

 were constantly preserved that had the longest tubes, 

 because they kept out mischievous visitors and so were 

 most frequently fertilised and left most progeny, there 

 must have been a corresponding selection among the 



