MUTATIONS AND THE GEOGRAPHIC DISTRIBUTION 

 OF NEARLY RELATED SPECIES IN PLANTS 

 AND ANIIVIALS 



J. A. ALLEN. 



In the American Naturalist for April, 1907 (vol. XLI, pp. 207- 

 240) Robert Greenleaf Leavitt has discussed with great clearness 

 and discrimination "The Geographic Distribution of Closely 

 Related Species," with more special reference to plants than to 

 animals, and also with reference to the bearing of the facts of dis- 

 tribution upon the mutation theory of de Yries. After present- 

 ing an impressive array of facts regarding the distribution of nearly 

 related species, or "forms," in several widely different groups of 

 plants, in part based on his own studies of the Orchidaceae, he 

 gives his personal impression of the matter, stating in his conclud- 

 ing remarks that it seems to him "that the study of specific distri- 

 bution in the vegetable kingdom is not likely to be unfavorable 

 to Mutation, regarded as a method, but perhaps not the sole 

 method, of evolution." He concludes: "The indications are 

 that the adherents of INIutation will be able to bring forward 

 enough cases of social distribution to render phytogeographic 

 weapons useless in the attack upon this Theory." 



Taking the facts of animal geography, as stated by a large 

 number of zoologists, "we may say," says Leavitt. "that as a 

 whole they militate against the operation of :\rutati()n in a wide 

 sense in the animal kingdom. This conclusion," he adds, "is 

 not prompted by the attitude of certain of the zoologists mentioned 

 . . . .but is drawn from the geographic evidence." 



In his final generalizations he offers this ver\^ judicial statement: 



opposed to oiirh other in their views of the actual >tate of sj.ecilic 



discover the condition and interj)ret its meaning among ain'nials, 

 and botanists among plants. In no case is it safe to reason deihic- 



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