688 



SCIENCE. 



[N. S. Vol. XXIII. No. 592. 



ties,' and are comparable to the water per- 

 sicaria and polycephalic poppies. 



Weismann speaks of Nageli's experi- 

 ments on Hieracium. He says : 



Many climatic varieties of plants may also be 

 due wholly or in part to the simultaneous variation 

 of corresponding determinants in some part of 

 the soma and in the germ-plasm of the reproduc- 

 tive cells, and these variations must of necessity 

 be hereditary. Temperature, and nutrition in its 

 widest sense, affect the whole body of the plant 

 — the somatic as well as the germ-cells. 



De Vries shows that the species of 

 Hieracium studied by Nageli exhibit the 

 phenomena of double adaptation. There 

 is no evidence that this attribute is origin- 

 ated by the direct influence of physical 

 environment. 



Although we have ample grounds for 

 doubting the validity of the assumption of 

 the adherents to the dynamic theory, we 

 can not yet refuse their hypothesis respect- 

 ful consideration. 



3. The de Vries Mutation Hypothesis. — 

 This hypothesis rests upon a negative and 

 a positive basis. The former is the nega- 

 tion of the ability of the two preceding 

 hypotheses to account for the origin of spe- 

 cies, affirming that fluctuating variation is 

 only between definite limits with reference 

 to a mean, and that environment does not 

 directly modify species. The positive ele- 

 ment is the observation of new forms 

 arising from older ones by mutation. Each 

 of these conclusions of de Vries is open to 

 challenge. (1) Have sufficient data been 

 accumulated to justify our discarding the 

 hypothesis that new species may originate 

 by the gradual accumulation of variations 

 that tend in a certain direction? (2) Is 

 the evidence submitted sufficient to war- 

 rant the permanent rejection of the dy- 

 namic hypothesis? (3) Are his supposed 

 mutations really mutations? The parent- 

 age of his Oenothera lamarckiana is not 

 known. May not his new CEnotheroe be 

 hybrids of some kind ? 



These different hypotheses present dif- 

 ferent explanations of phenomena assumed 

 to be true by each one. I think that they 

 render necessary a more critical analysis 

 of the biological facts cited to substantiate 

 each one. 



At the last meeting of this society Dr. 

 Merriam presented a paper, 'Is Mutation a 

 Factor in Evoliition ? ' His facts were that 

 various regions are inhabited by subspecies 

 of mammals or birds in accordance with 

 their differences in physical conditions, and 

 that the transition zone between two re- 

 gions is occupied by intergrading forms. 

 Take, for instance, two adjacent areas pre- 

 senting different physico-geographic char- 

 acters: one subspecies would be found in 

 one area; in the other area, another sub- 

 species. The physical conditions in going 

 from one area to the other do not change 

 abruptly, but gradually. The intermediate 

 zone is not only intermediate in physical 

 characters, but is occupied by individuals 

 that are intermediate in their characters 

 between the subspecies of the two different 

 areas. As Dr. Merriam quoted the ham- 

 mer and anvil simile of Dall, we are, I 

 think, justified in placing him in the cate- 

 gory of the dynamic evolutionists. His 

 conclusions were : 



1. There is evidence of the intergrada- 

 tion between species. 



2. The direct influence of environment 

 is the principal factor in the production of 

 new species. 



3. In the higher vertebrates there is no 

 evidence of the origin of species by 'mu- 

 tation.' 



As to Dr. Merriam 's statements regard- 

 ing the classification and distribution of 

 the animals discussed in his communica- 

 tion, we can say nothing, for all of us know 

 of the many years that he has spent collect- 

 ing and studying them and plotting their 

 distribution with reference to geographic 

 conditions. But I think his explanation 

 of the phenomena open to question. 



