What is a species? 



T. D. A. COCKERELL 



On reading Dr. Gleason's comments on species on pages 43-45 

 of the March-April number of Torreya I feel that his philosophy 

 (perhaps not intended to be taken too seriously) is wrong. He says : 

 "Suksdorf may or may not be justified in making so many species." 

 Suksdorf, in my judgment, never made a species in his life; he 

 only described what he supposed were species. Miintzing and Er- 

 lanson may be said to have made species, in the manner indicated 

 below. Then Dr. Gleason offers a definition : "A species is a group 

 of one or more individuals which in your opinion deserves a bi- 

 nominal name." To me species are objective realities in nature, and 

 subjective opinions do not in the least affect their existence or 

 number. But, it may be replied, is not the conception of a species 

 a product of the human mind, and do not as a matter of fact the 

 number of species differ with the opinion of botanists? Thus 

 Miintzing, in a recent discussion of the cytology of Potentilla, states 

 that P. argentea L. has different chromosome-races within the spe- 

 cies. There are diploid, hexaploid and octoploid races. These plants 

 also differ in appearance, yet Miintzing concludes that "there seems 

 to be no reason to split P. argentea into a great number of 'species' 

 of the Hieracinm type, though this might certainly be easily done." 

 Perhaps someone will do it, and then the number of species of 

 Potentilla will appear to rest, not on the actual facts, about which 

 there is no dispute, but upon the opinion of this or that botanist. 

 However, the ordinary conception of a species is that of a group of 

 individuals remaining normally isolated in nature, and exhibiting 

 special specific characters. This is a loose definition, but sufficient 

 to cover the various aspects of the subject. Among insects, which 

 are more specialized and standardized than plants we find pairs of 

 species which are so much alike that it is difficult for experts to 

 distinguish them, yet observaton shows them to be quite distinct 

 entities in nature. We also find cases where the ranges of related 

 species meet and crossing occurs. Among plants, it is easy to see 

 that apparently good species may be dissolved into a variable hybrid 

 population. A very good case is that of the blue Aquilegia caerulea 

 and the yellow A. chrysantha. As they exist in nature, occupying 

 different ranges, they are excellent species. But in gardens they 



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