HOW PLANTS CAME TO DIFFER. 31 



honey. In eating it, they would dust themselves 

 over with the floury pollen, by pure accident, and 

 they would carry some of it away with them on 

 their heads and legs to the next flower they 

 visited. Chance would make them often rub off 

 the pollen and fertilise the flower ; and as such 

 cross-fertilisation, as it is called, is good for the 

 plants, producing very strong and vigorous seed- 

 lings, the young ones so set would have the best 

 chance of flourishing and surviving in the Struggle 

 for Existence. Thus the flowers which made most 

 honey would be oftenest visited and crossed, so 

 that they would soon become very numerous. 

 Again, if they happened to have bright leaves 

 near the honey, they would be most readily dis- 

 criminated, and oftenest visited. So, in the long 

 run, it has come about that almost all the flowers 

 fertilised by insects produce honey to allure them, 

 and have brilliant petals to guide their allies to 

 the honey. That, in fact, is what beautiful flowers 

 are for — to attract the fertilising bees and butter- 

 flies to visit and impregnate the various blossoms. 

 Take one more case — or, rather, the same 

 case, extended a little further. The red cam- 

 pion flowers by day, and is fertilised by butter- 

 flies ; therefore it is pink, because pink is an 

 attractive colour in the daylight; and it is scent- 

 less, because its colour alone is quite enough to 

 attract sufficient insects. But it has a close rela- 

 tion, the white campion, which flowers by night 

 only, and lays itself out to be visited by moths in 

 the twilight. Why is this kind white ? Because 

 no other colour is seen so well in the dusk ; a red 

 or pink blossom would then be almost invisible. 

 Moreover, the white campion is heavily scented, 

 as are almost all other night-flowering blossoms, 



