﻿VOLUME LXI 



NUMBER 3 



THE 



Botanical Gazette 



MARCH 1916 

 ON PAIRS OF SPECIES 



Reginald Ruggles Gates 

 (with TWELVE figures) 

 Our growing knowledge of the definiteness of variation makes it 

 desirable that botanists should begin to apply this knowledge to a 

 more detailed study of the relationships of particular species. With 

 this end in view I have endeavored to begin such a study by the 

 examination of the various relationships between pairs of species 

 in the same genus. Every botanist knows numbers of such cases, 

 and it occurred to me that it would be worth while to analyze 

 several such pairs as regards their differential characters, habitats, 

 and distribution, to discover whether any light can be thrown in this 

 way on the probable origin of the species in question. How have 

 these differences arisen in the light of our present views of varia- 



Again, various rules of distribution have been proposed, such 

 as Jordan's law that related species occupy adjacent areas. It is 

 not the purpose of this paper to discuss questions of distribution at 

 any length, but it will be seen incidentally that a species and its 

 next of kin may occupy (1) the same locations, (2) adjacent areas, 

 or (3) widely separated regions. They may overlap, or the dis- 

 tribution may be practically coterminous. From such facts as these 

 it might appear that Jordan's law as applied to plants is more 

 honored in the breach than in the observance; but when applied 

 to the variations or tendencies to variation within the taxonomic 

 species, every botanist knows how usually it holds as modified by 



