VARIATION IN PEDIGREE-CULTURES 209 



thing that Dr. Merriam has put into print concerning his extensive 

 and thorough field work in the west, and that I vield to none in mv 

 admiration of the wide inclusiveness of his results and the profitable 

 manner in which he has treated incidentally the general features of 

 the occurrence and distribution of plants. This appreciation is 

 heightened by the fact that I have spent many seasons in the regions 

 covered by him during the last fifteen years, and that I have carried 

 on experimental work in the field and at the Desert Laboratory with 

 many of the species which are included in his generalizations. I have 

 not been able to come upon the evidence, or record of evidence, upon 

 which his sweeping statements relative to plants are based, although 

 detailed studies upon the relation of plants to environmental factors 

 have been in progress for some time. 



Dr. Merriam does not find any evidence to support the conclusion 

 that species arise by mutation. It would be a matter of great sur- 

 prise if he had. It would be as reasonable to have demanded of him 

 the solutions of problems of respiration from his preparations and 

 field notes. Once a mutant has appeared, no evidence of its distribu- 

 tion can be taken to account conclusively for its origin. Although I 

 have had many mutants under experimental observation, I should not 

 be able to speak with reasonable certainty as to the origin of any of 

 them, had I not ascertained it by guarded pedigree-cultures. It also 

 follows that the systematists who announce and describe new forms as 

 mutants, simply from preserved specimens, or from individuals, the 

 origin of which is not a matter of careful observation, are following 

 a wholly unwarranted practise. Several months ago I had occasion 

 to say " that the ' naturalists,' as some zoologists term themselves, 

 having made the greatest number of essays to offer a universal interpre- 

 tation of the problems of distribution, are to be credited with the 

 greatest number of defenseless assumptions. In all genetic and evolu- 

 tionary researches too much emphasis can not be laid upon the basal 

 fact that the physiological and morphological natures of the two great 

 classes of living things are so widely divergent that the derivation of 

 universal biological principles from their apparently concurrent be- 

 havior must be made with the greatest caution." Nowhere does this 

 find better exemplification than in the unedifying results of a recent 

 discussion of isolation as a factor in evolutionary action. A number 

 of zoologists have assumed to speak of the distribution of plants, with 

 apparentlv no basis except ' general information ' to the effect that 

 closelv related species do not have the same habitat. This has been 

 variously put, but the general meaning is as given. Now such a 

 conclusion is so widely inapplicable, and is so loosely guarded, as to 

 be wholly without value as a statement of a principle in plant 



VOL. LXIX. — 14. 



