GUELDER ROSE. 95 



guelder rose. In daisies and sunflowers, the 

 outer florets of each head have their petals pro- 

 longed into pink-tipped or golden rays, which 

 give the compound bunch much the appear- 

 ance of a single blossom. In cow-parsnip 

 and most other umbellates the two outer 

 petals of all the external flowers grow much 

 bigger than their three inner petals, so as 

 greatly to increase the total conspicuousness 

 of the whole bunch. Whenever the separate 

 blossoms of a plant have grown so small as 

 to be individually little attractive, they will 

 clearly gain an advantage by detailing some 

 of their number to do special duty as adver- 

 tisements. But it seems difficult at first 

 sight to see how natural selection can bring 

 about such a result. Mr. Herbert Spencer 

 has pointed out the way out of this difficulty. 

 If you look at a cow-parsnip, you will see 

 that the crowded central flowers of each head 

 are very small, with cramped petals, because 

 they have no room to expand without crush- 

 ing one another; but the freer external 



