No. 484] 



CLOSELY RELATED SPECIES 



237 



CoxcixDiXG Remarks. 



In concluding this paper I may make some remarks of a general 

 character touching the whole prohlem. 



First, we note that zoologists and botanists are rather distinctly 

 opposed to each other in their views of the actual state of specific 

 distribution. The suggestion is offered that zoologists may best 

 discover the condition and interpret its meaning among animals, 

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

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

 their evolution plants and animals differ vastly. 



Secondly, in seeking for the laws of specific distribution we 

 should first take the facts as we find them. We should acrree 

 to consider that in the absence of explicit evideucc to tli<> coiin-ary, 

 kinds now found in coincident ranges have been so situated from 

 the beginning. In any given cases this assumption may or may 

 not represent the truth, but we have no right to postulate move- 

 ments in the past, of which there is no certain evidence, in order 

 to save a preconceived theory. We may call sucli hyj)oth(>tical 

 migrations into being, in a strictly hmitcd number of ( mm's. \ipon 

 a reconsideration, if from a first cxaininaiioM ot the unuio.hlied 

 facts some law emerges so strong and com])ulsory that the few 

 exceptional instances must somehow be brought into Jiccord with 

 it. 



In the third place, if I may express my personal iniy)ression of 

 the matter with regard to plants, it seems to me that tlie sttidy of 

 specific distribution in the vegetable kingdom is not hkely to be 

 unfavorable to Mutation, regarded as a method, but ])erhaps 

 not the sole method, of evolution. It is true that in examining 

 the distribution of species of plants, one encounters an effect 

 which seems to be connected with geographical (h>iant'e. \Veoftt>n 

 find that a species of wide distribution exhil)its shghtly (htferent 

 phases in different divisions of its range. These phases are some- 

 times too subtle for definition and pass into one another by degrees, 

 yet are evident to students of particular groups. Such cases do 

 not look like the work of Mutation. They exemplify that which, 

 to conceal ignorance of causes, may be termed a geographic effect. 



