CHAP. X. CROSS-FERTILISATION. 383 



amount of pollen which is always incoherent, and 

 in the stigma often being largely developed or 

 plumose. We certainly owe the beauty and odour of 

 our flowers and the storage of a large supply of honey 

 to the existence of insects. 



On the Relation between the Structure and Conspicuous- 

 ness of Flowers, the Visits of Insects, and the Advan- 

 tages of Cross-fertilisation. 



It has already been shown that there is no close 

 relation between the number of seeds produced by 

 flowers when crossed and self-fertilised, and the degree 

 to which their offspring are affected by the two pro- 

 cesses. I have also given reasons for believing that 

 the inefficiency of a plant's own pollen is in most cases 

 an incidental result, or has not been specially acquired 

 for the sake of preventing self-fertilisation. On the 

 other hand, there can hardly be a doubt that dichogamy, 

 which prevails according to Hildebrand* in the greater 

 number of species, that the heterostyled condition of 

 certain plants, and that many mechanical structures 

 have all been acquired so as both to check self- 

 fertilisation and to favour cross-fertilisation. The 

 means for favouring cross-fertilisation must have been 

 acquired before those which prevent self-fertilisation ; 

 as it would manifestly be injurious to a plant that 

 its stigma should fail to receive its own pollen, 

 unless it had already become well adapted for receiv- 

 ing pollen from another individual. It should be 

 observed that many plants still possess a high power 

 of self-fertilisation, although their flowers are excel- 

 lently constructed for cross-fertilisation for instance, 

 those of many papilionaceous species. 



* ' Die Geschlechter Vertheilung,' &c. p. 32. 



