400 



SCIENCE. 



[N. S. Vol. XXIV. No. 613. 



surely ' real ' species, whether other forms 

 called species are ' real ' or not. We find no 

 evidence that such species could not or do not 

 originate, sometimes at least, through slight 

 fluctuations acted upon by selection in segre- 

 gation. We do not know that the effects of 

 selection have any final limit except in certain 

 cases where the limit is mechanical. It is 

 not yet clearly shown that there is any real 

 and fundamental difference between contin- 

 uous and discontinuous variation, and most 

 zoologists regard the conception and cycles 

 of variation in the history of a species as an 

 ingenious suggestion rather than as a part 

 .of science. 



It is evident that there is much — very much 

 — about animals and plants, which can be 

 learned only from experimentation under 

 ■ changed conditions, as there is much that can 

 not be known or even imagined without the 

 aid of the microscope, and much that can not 

 be known or imagined without the compara- 

 tive study of many individuals and the com- 

 parison of faunal and floral areas. We must 

 welcome the study of pedigreed individuals, 

 animals or plants, as a raost hopeful line of 

 investigation, and it is certain that the dis- 

 coveries it may yield can not be forestalled 

 in advance. If they could the investigation 

 would be unnecessary. So far as species are 

 concerned, it is clear that a large part of the 

 problem demands the study of the structure of 

 forms and their relation to environment. 

 There is much truth in Darwin's words that 

 "One has hardly a right to examine the ques- 

 tion of species who has not minutely described 

 many." 



As to the suggestion of the possible hybrid 

 origin of CEnothera, the writer is not a 

 botanist, and very much of botanical investi- 

 gation escapes his notice. He is pleased to 

 learn that the possibility of such origin on 

 the part of (Enothera lamarcMana has been 

 considered and fully disproved. A detailed 

 account of the experiments which show this 

 would be interesting. It would also be inter- 

 esting to know the degree in which Burbank's 

 hybrid walnuts of the second generation, show- 

 ing ' every conceivable kind of variation,' con- 

 form to the Mendelian theory. 



As to the theory that species are permanently 

 changed by the direct impact of environment, 

 which most faunal zoologists in America seem 

 to accept, the writer thinks that Dr. Mac- 

 Dougal is probably right in claiming that " no 

 evidence has yet been obtained to prove that 

 the influence of tillage, cultivation or the 

 mere pressure of environmental factors has 

 produced any permanent changes in hereditary 

 characters of unified strains of plants," or of 

 animals either. 



David Starr Jordan. 



vulcanism. 



I HAVE read the article of Elihu Thomson,* 

 much of which is necessarily true, with con- 

 siderable interest; but I doubt whether I can 

 go so far as he does, partly because I have a 

 pet theory of my own to nurture. What I miss 

 in Thomson's article is some definite estimate 

 or clear-cut specification of the actual condi- 

 tions involved: how much stuff is moved; 

 what work is spent; how much heat is gener- 

 ated. I have endeavored to picture the occur- 

 rences to myself in a cursory way for a nor- 

 mal case, somewhat as follows : The work done 

 per cubic centimeter will in any distortion be 

 half the product of the stress and the strain. 

 This work will be elastically potentialized if 

 the solid remains intact. If there is rupture 

 it will appear as heat largely near the surface 

 of separation. If it yields viscously (as is 

 much the more probable) it will appear 

 throughout the volume. The strain is prob- 

 ably a shear. The question at issue is then 

 under what circumstances of torment must 

 one shear a rock in order to melt it. Suppose 

 we say the shear is one half, i. e., if the tan- 

 gential thrust is horizontal all initially ver- 

 tical lines will be inclined thirty degrees; or 

 in general there will be corresponding changes 

 of inclination of thirty degrees, which seems 

 to me to be enormous, but may, nevertheless, 

 be admitted for the purpose of argument. 

 We may then write, if the density of rock is 

 3, its specific heat .2, its igneous melting point 

 as low as 1,000° C, 



1/3 X 1/2 X ^ = 3 X .2 X 1000 X 42 X 10«, 



^ Science, XXIV., p. 161, 1906. 



