No. 510] PROBLEMS IN PLANT ECOLOGY 



of evolution was never more evident in the past than it 

 is to-day. The work of Klebs has opened up almost limit- 

 less possibilities along such lines. The intrinsic theories 

 of evolution, such as orthogenesis and heterogenesis (or 

 mutation) are also vigorously maintained. All such 

 theories, both extrinsic and intrinsic, appear to be in 

 harmony with the present results of ecological research, 

 and the future alone may say whether some or all of these 

 and more are true. 



To the working ecologist the necessary consequences 

 of the abandonment of the idea of adaptation and of nat- 

 ural selection as a causative factor are most vital. First 

 and foremost there comes the possibility of disad- 

 vantageous trends in evolution. To some extent such 

 tendencies will be checked by the destructive operation 

 of natural selection, so that only such new species as are 

 most fit are likely to survive and have progeny. But in 

 view of the ideas that have generally prevailed in past 

 years, it can not be emphasized too strongly that plants 

 may retain useless structures and even structures that 

 are moderately harmful, and yet live on if they also 

 possess other structures or habits that are sufficiently ad- 

 vantageous. This conception at once relieves ecologists 

 of one of the most arduous of their former duties, the 

 establishment of an advantageous function for every or- 

 gan, and of a benefit in every function. The chapters on 

 the uses of palisade cells, crystals, poisons, latex and the 

 myriad kinds of hairs are likely to be shorter and less 

 dogmatic in future ecological treatises. Even such or- 

 gans as stomata are apparently being divested of their 

 erstwhile most important function, the regulation of 

 transpiration. 



It has been so long the fashion to regard the various 

 kinds of floral structures as most useful that it may be 

 thought ecological heresy to question their utility. The 

 intimate correlation between the evolution of the insect 

 and the flower was such a pretty story that it seems rude 

 to question it, but do we have any adequate evidence of 



