654 



THE AMERICAN NATURALIST 



[Vol. XLI 



tively from one kingdom to the other. In the factors affecting 

 their evolution plants and animals differ vastly." 



Here is a concession from the side of the botanists that should 

 do much toward harmonizing the conflicting views of botanists 

 and zoologists respecting the influence of ' mutation ' in the evolu- 

 tion of forms among animals and plants. In the first place the 

 conditions of reproduction, structure, growth, etc., in the two 

 kingdoms are so radically different that the methods of evolution 

 may also well be different; indeed, it would be surprising to find 



Mr. Leavitt's paper is primarily a contention that President 

 Jordan's law respecting the distribution of nearly related species 

 does not hold in the vegetable kingdom. It is assumed that Jor- 

 dan's law was intended to apply ecjually to l)oth animals and plants, 

 which interpretation seems to be supported by the context of the 

 paper. The law is as follows: "Given any species in any region, 

 the nearest related species is not likely to be found in the same 

 region nor in a remote region, but in a neighboring district sepa- 

 rated from the first by a barrier of some sort." If we substitute 

 in this expression the word 'kind' or 'form' in place of 'species,' 

 and restrict its application to animals, it will probably meet with 

 general approval on the part of zoologists. 



In testing Jordan's law by an examination of the facts of dis- 

 tribution presented by the Orchidaceae, Leavitt says he "looked 

 for pairs of kinds," and atids: "I say kinds instead of species 

 intentionally. The main problem should not be confused by the 

 diflBculty of agreeing ujxjn a definition of species. What the evo- 

 lutionist has to account for is not the definitions of systematists, 

 but the nmltiplicity of hereditary types; he has to explain the 

 antithesis between the uniformity which heredity seems at first to 

 promise, and the diversity which actnally prevails among organic 

 tln'riiis." It i- cvi.h-nt, liowcvcr. that in the ("XjH-ession "pairs of 



(iiflVrfnt iii-taiico, and is not here the iMiuivalent of " nearly related 



As rcaanls the hiuhcr \ fHcbratrs, the rviilcncc is indisputable 

 that t\v., closely rrlat(Ml f..nns do not o.cni-y the same area. By 

 this expression the subspecies of zoologists are meant, — in other 



