THE ORIGIN OF NEW FORMS 201 



different times. The writer's own studies have demonstrated 

 that this is equally true of ecads. In consequence, the conclusion 

 is unavoidable that it holds equally well for variants, since the 

 conditions that bring about variation and selection would recur 

 at various points in the area of a species widely distributed. 



A form that arises in two or more places is called polytopic, 

 one originating at different times, polychrome. Contrasted with 

 these are monotopic forms which originate but once. On account 

 of migration, it is practically impossible to determine whether a 

 species is polytopic or monotopic except by experiment. It is 

 equally impossible to tell at present which method is the usual 

 one, though it is probable that most forms are monotopic. 



214. Experimental evolution. Three fundamental methods 

 form the basis of the experimental study of evolution,^ which 

 alone can yield trustworthy results. The first makes use of the 

 actual experiments in adaptation, mutation, hybridation, and 

 variation which are found in nature. The second produces similar 

 experiments in nature, either by changing the habitat in which 

 the form concerned is found, by transferring the plant to new 

 and different habitats, or by actual crossing. The third method 

 is a modification of the last, by which plants are brought into 

 the greenhouse and subjected to known factors, which are kept 

 under control. While these methods of experimental evolution 

 seem simple, they are out of place in an elementary study of 

 ecology. The origin of a new form is so complex and such thorough 

 anfl painstaking study is required, that experiments of this sort 

 must be left to the specialist. 



Research Methods, 149. 



