LA W OF PROGRESSIVE CCLO URA TION. 1 9 



nettles exclusively. Fritz Miiller noticed a Lantana in 

 South America which changes colour as its flowering 

 advances ; and he observed that each kind of butterfly 

 which visited it stuck rigidly to its own favourite colour, 

 waiting to pay its addresses until that colour appeared. 

 Mr. Darwin cut off the petals of a lobelia and found that 

 the hive-bees never went near it, though they were 

 very busy with the surrounding flowers. But perhaps 

 Sir John Lubbock's latest experiments on bees are 

 the most conclusive of all. He had long ago con- 

 vinced himself, by trials with honey placed on slips of 

 glass above yellow, pink, or blue paper, that bees 

 could discriminate the different colours ; and he has now 

 shown in the same way that they display a marked 

 preference for blue over all other hues. The fact is, 

 blue flowers are, as a rule, specialised for fertilisation 

 by bees, and bees therefore prefer this colour ; while 

 conversely the flowers have at the same time become 

 blue because that was the colour which the bees 

 prefer. As in most other cases, the adaptation must 

 have gone on pari passu on both sides. As the bee- 

 flowers grew bluer, the bees must have grown fonder 

 and fonder of blue ; and as they grew fonder of blue, 

 they must have more and more constantly preferred 

 the bluest flowers. 



We thus see how the special tastes of insects may 

 have become the selective agency for developing 

 white, pink, red, purple, and blue petals from the 

 original yellow ones. But before they could exercise 

 such a selective action, the petals must themselves 

 have shown some tendency to vary in certain fixed 

 directions. How could such an original tendency 

 arise? For, of course, if the s insects never saw any 



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