Ctickoo-Piiit. 257 



nation ; and, crawling over them in an aimless sort of 

 fashion, they rub off upon their sensitive surfaces 

 some of the pollen which they brought with them 

 from the last plant they visited. This pollen thus 

 cross-fertilises the fruit, and produces in it seeds 

 which are the product of two distinct parents, and 

 therefore capable of springing up into vigorous seed- 

 lings of the strongest sort. 



But though the small flies have thus benefited the 

 plant by fertilising its ovaries with pollen brought 

 from another head, they have as yet got no return for 

 their trouble in the shape of meat or drink : and, 

 unless they did so, they certainly would not take the 

 trouble to visit any other flower of the same sort. 

 The stamens are not yet ripe, and do not ripen until 

 after the pistils have set their fruit. If they did 

 otherwise, then the pollen would fall from them down 

 upon the sensitive surfaces of their sister blossoms 

 below, and the plant would accordingly be self- 

 fertilised— a thing to be alwa}-s avoided as far as pos- 

 sible. Accordingly, it is a fi.Kcd rule in the cuckoo- 

 pints that the pistils, which are below, come to 

 maturity first, while the stamens, which are above, 

 shed their stock of pollen a day or two later. This 

 being so, the flies find nothing in the new flower to 



detain them any longer ; and, if they could, they 

 12 



