104 NATURE STUDIES. 



towards the centre. At this early stage, however, 

 the carpels are not yet mature for impregnation, and 

 so they avoid being fertilised from the pollen of their 

 own stamens. If the bee flies away to another butter- 

 cup which happens to be still in the same stage of 

 development, he only collects more pollen about his 

 head and thighs ; but if he alights on a somewhat 

 older buttercup, he finds its stamens withered and its 

 carpels fully mature for impregnation. Some of the 

 pollen is then sure to fall on the sensitive surface of 

 the carpels. Thus, while he seeks honey for himself, 

 he unconsciously affords his host all the advantages of 

 cross-fertilisation; and it is because he does so that 

 the flower has been enabled to develop its complicated 

 arrangement of petals and nectaries for his delectation. 

 The buttercup, then, with its five separate simple 

 petals, its many stamens, and its central one-seeded 

 carpels, may be regarded as a good example of the 

 earliest type of insect-fertilised flowers. In some 

 other plants, such as the harebell and the primrose, 

 the separate petals have coalesced into a single tubular 

 corolla; while in others, again, they have assumed 

 various fantastic shapes ; but all of them are ultimately 

 derived from flowers like the buttercup, which thus 

 contains in itself all the essential elements of a perfect 

 insect-fertilised plant. 



