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THE AMERICAN NATURALIST [Vol. XLIII 



advantage in the myriad diversity seen in flowers, much 

 less any advantage great enough to have been of sig- 

 nificance in directing to any notable degree the trend of 

 evolution? It is usually assumed that dichogamy, hetero- 

 styly, prepotency of foreign pollen, and zygomorphy are 

 advantageous characters because they promote cross 

 pollination or pollination by special insects, but the facts 

 on which such conclusions are based are verj^ slender. 

 There are many plants which are regularly close-polli- 

 nated and they seem to succeed as well as others. The 

 Composite are often regarded as the highest of the seed 

 plants, and they are of especial interest because they are 

 a group that is ecologically successful as well as morpho- 

 logically advanced, features that often fail to coincide 

 elsewhere. But the Composite show comparatively little 

 zygomorphy or insect selection; as a group they are 

 notably geitonogamous or even autogamous, and yet none 

 of the supposed disadvantages of close pollination are 

 evident. Indeed the massing of flowers in heads and the 

 consequent facilitation of pollination between near-by 

 flowers may be one of the reasons for their great success. 

 But there are reasons for believing that any or all kinds 

 of pollination are vastly inferior to vegetative reproduc- 

 tion in determining the success of a group. The notable 

 success of the grasses and sedges is doubtless due to their 

 rhizomes far more than to their flowers, and in the duck- 

 weeds and many aquatics the flower has become almost 

 a negligible quantity. Such considerations make it at 

 least doubtful whether many conspicuous floral structures 

 possess the great advantages in the life of plants that 

 have been commonly ascribed to them. 



The conception that plant structures may often have 

 originated quite independently of any important use or 

 function, or even independently of any environmental 

 influence is useful at many points. It explains how there 

 can exist the phenomenon of " over-adaptation," which 

 appears to be exhibited in the orchid flower and in the 

 testa of many xerophytic seeds. It makes possible a new 



